Immunology Questions

A 4-year-old boy consumes garden soil, grass, and water. Despite the presence of several species of bacteria within the soil, this boy's intestines were not colonized by the ingested bacteria. Which is the most likely explanation for this lack of colonization? a. Acid in his stomach kills the bacteria before they enter the intestines b. Lactose in the milk he drank kills the bacteria in his gut c. IgE produced in response to peanut ingestion inhibits growth of the bacteria d. Unfavorable environmental conditions kill the bacteria before he eats them e. Soil bacteria are digested and quickly eliminated along with food from his lunch

a. Acid in his stomach kills the bacteria before they enter the intestines Explanation: Hydrochloric acid in the stomach decreased the stomach pH and makes it an unsuitable environment for microbial growth. In addition, IgA, not IgE will bind to microbes and prevent microbial attachment and invasion into the mucous membranes.

The classical pathway of complement begins with which action? a. Activation of C1 b. Cleavage and activation of C4, C2, and C3 c. IgA binding to a specific epitope d. Initiation of membrane attack complex formation e. Production of C3 convertase

a. Activation of C1 Explanation: The classical pathway of complement begins with the recognition of antigen-antibody complexes by the first component of complement, C1. Subsequent steps in the classical pathway involve activation of components C4, C2, C3, and the production of C3 convertase leading to the production of C5 convertase and entry into the membrane attack complex. Antigen binding by IgA does not activate the classical pathway.

The role of terminal deoxynucleotidyl transferase (TdT) in development of antibody diversity is to? a. Add/remove nucleotides of V, D, and J genes b. Fuse VD and J segments together in heavy chains c. Increase binding affinity of antibody for antigen d. Join CL to CH1, CH2, CH3, or CH4 domains e. Transfer VL alleles from maternal to paternal chromosomes

a. Add/remove nucleotides of V, D, and J genes Explanation: TdT adds or removes nucleotides when the ends of V, (D), and/or J gene segments are exposed. This process, known as junctional diversity, occurs during DNA rearrangement.

Serum immunoglobulins containing both maternally and paternally derived light chains are found within an individual. A given B cell, however, expresses only maternally derived or paternally derived chains but never both. This finding is the result of? a. Allelic exclusion b. Antibody diversity c. Isotype switching d. Junctional diversity e. Random VD and VDJ joining

a. Allelic exclusion Explanation: A given B cell or plasma cell expresses a single maternal or paternal allele of a chromosome pair. This process, known as allelic exclusion, applies to both heavy and light chain genes. Isotype switching, junctional diversity, and random V(D)J joining occur after allelic exclusion.

A 57-year-old Hispanic man presents to the office with a severe cutaneous rash over his back that has developed over several weeks and intractable watery diarrhea. One month earlier he was diagnosed with adult T-cell leukemia and received a bone marrow transplant from an unrelated donor. Laboratory tests show: Alanine aminotransferase: 1032 U/L Aspartate aminotransferase: 829 U/L Creatinine: 1.0 mg/dL Lactate dehydrogenase: 634 U/L Alkaline phosphatase: 446 U/L Which of the following is most directly responsible for this patient's current presentation? a. Alloreactive donor T-cells b. Immunoglobulins and fibrinoid necrosis c. Recipient antigen-presenting cells presenting donor peptides d. Recipient cytotoxic T-cells

a. Alloreactive donor T-cells A patient that presents with an erythematous rash, diarrhea, and elevated liver function tests after a bone marrow transplant most likely has GVHD. GVHD is a type IV hypersensitivity reaction due to grafted donor immunocompetent T-cells that reject host cells.

A 9-year-old girl is stung on her arm by a bee. The first time she was stung was 2 years ago, the sting site was painful and became swollen but resolved uneventfully. This time, however, widespread urticaria (hives) develops soon after the sting. She also develops facial edema and reports difficulty breathing. This patient has most likely experienced? a. Anaphylaxis b. Antibody-mediated toxicity c. Contact sensitivity d. Serum sickness e. Type II hypersensitivity

a. Anaphylaxis The symptoms described are those of anaphylaxis which is a type I hypersensitivity

A 72-year-old man is brought to the emergency department with respiratory difficulty and severe circumoral, periorbital, and facial edema. He was recently prescribed atorvastatin, metoprolol, and captopril. Accumulation of which of the following substances is most likely causing the patient's symptoms? a. Bradykinin b. Histamine c. Prostacyclin d. Prostaglandin E2 e. Serotonin

a. Bradykinin Explanation: ACE inhibitors may cause angioedema in the face, lips, mouth, and subglottic tissues. Angioedema occurs due to the accumulation of bradykinin.

Isotype switch is an important mechanism by which the immune system tailors the response to the appropriate attack on a pathogen. Which of the following cytokines is important for promoting isotype switch to IgE? a. IL-4 b. IL-10 c. IL-17 d. IFN-γ e. TGF-β

a. IL-4 Explanation: IL-4 is the most potent cytokine for promoting isotype switch, especially to IgE. IL-17 and IFN-γ stimulates IgG production and TGF-β will stimulate IgA production.

Which of the following is most likely to induce the greatest immune response? a. 250,000-Da plasma self protein b. 150,000-Da toxin produced by bacteria c. 500-Da simple peptide d. A protein with several epitopes buried in its interior

b. 150,000-Da toxin produced by bacteria Explanation: Bacterial toxins are often very immunogenic. An individual should normally not make adaptive immune responses against her or his own self proteins. A protein with numerous diverse epitopes is more likely to induce an immune response than a simple peptide, however, the epitopes must be readily accessible to be immunogenic.

A 25-year-old female was given a single injection of penicillin for the treatment of syphilis. Within minutes, she developed diffuse urticaria, tachycardia, and hypotension. What is this reaction called? a. Anaphylaxis b. Anergy c. Antibody-mediated cytotoxicity d. Sepsis e. Contact dermatitis

a. Anaphylaxis This individual displays the hallmarks of a classical anaphylactic reaction to penicillin. Anergy is the impairment of effector immune responsiveness. Antibody-mediated cytotoxicity is most often localized to tissues bearing epitopes to which the antibody binds. Contact dermatitis results from the epicutaneous application of a reactive antigen/hapten; in the present question, the antigen (penicillin) was administered intramuscularly.

A 3-year-old male child with an X-linked defect in the Bruton tyrosine kinase (BTK) gene is impaired in which of the following mechanisms? a. Antibody-mediated bacterial clearance b. Formation of the membrane attack complex c. Isotype switching d. IFN-γ secretion by CD4+ T cells e. Ability to recognize self-antigens

a. Antibody-mediated bacterial clearance Explanation: Bruton agammaglobulinemia results in a near or total absence of B cells and immunoglobulins; hence, antibody-mediated responses to microbes are severely impaired. A BTK mutation prevents the B-cells from undergoing positive and negative selection and therefore, they cannot even progress towards self0antigen screening or isotype switching. Even in the absence of antibodies and the classical pathway of complement activation, the membrane attack complex can be generated through the MBL and alternative pathways. IFN-γ secretion by CD4+ T cells is not affected by antibodies.

An 8-year-old boy with sickle cell anemia is brought to the pediatrician by his mother because of a 10-day history of right leg pain. Temperature is 39°C (102.2°F). Physical examination shows swelling and erythema in the area over his right tibia. A culture of infected bone reveals infection with Salmonella. Which of the following factors predisposes this patient to his current infection? a. Asplenia b. No thymus c. No lymph node d. Dysfunctional bone marrow e. No tonsils

a. Asplenia Bone pain, redness, and swelling in a patient with sickle cell disease are suggestive of bacterial osteomyelitis. Patients with sickle cell disease are vulnerable to encapsulated bacteria, such as Salmonella and E coli, because of their loss of splenic function.

Which of the following is a primary lymphoid organ? a. Bone marrow b. Lymph node c. Peyer's patch d. Spleen e. Tonsil

a. Bone marrow The bone marrow is a primary lymphoid organ. Lymph nodes, Peyer's patches, spleen, and tonsils are all secondary lymphoid organs.

A 2-year-old girl is brought to the pediatrician by her mother for evaluation of a 2-day history of increasing irritability and fever. She has had recurrent ear and sinus infections. On physical examination, she has pale white hair and her irises are bluish-gray. Which of the following is the most likely diagnosis? a. Chédiak-Higashi syndrome b. Chronic granulomatous disease c. Leukocyte adhesion deficiency d. Selective IgA deficiency e. Severe combined immunodeficiency f. Wiskott-Aldrich syndrome

a. Chédiak-Higashi syndrome Chédiak-Higashi syndrome is an immunodeficiency that presents with impaired phagocytosis, partial albinism, and platelet defects due to a defect in microtubule polymerization.

A 4-year-old boy is brought to the emergency department with fever, cough, and dyspnea, worsening over the last week. He has a history of recurrent bacterial infections since birth and easy bruising and bleeding from gums. Physical examination shows speckled areas of hypo- and hyperpigmentation diffusely on his skin, with several areas of bruising. There are lower left lobe pulmonary crackles. The gait is abnormal. Laboratory values show a Hb of 10.2 g/dL, 3,500 WBCs/mcL, and 50,000 platelets/mcL. Chest x-ray shows a dense opacity in the left lower lobe. Peripheral blood smear is shown. Which of the following is the most likely cause of this patient's presentation? a. Chédiak-Higashi syndrome b. Chronic granulomatous disease c. Leukocyte adhesion deficiency (type 1) d. Severe combined immunodeficiency e. Hemophagocytic lymphohistiocytosis

a. Chédiak-Higashi syndrome Explanation: Chédiak-Higashi syndrome is an autosomal recessive disease characterized by a defect in phagosome-lysosome fusion. There are pyogenic infections with Staphylococcus and Streptococcus species, albinism, peripheral neuropathy, and progressive neurodegeneration. The photo shown contains neutrophils with abnormally chunky granules.

After receiving a kidney transplant from the most appropriate available donor, a 38-year-old female is administered immunosuppressive drugs, including cyclosporine, in order to? a. Decrease T-cell production of IL-2 b. Destroy stem cells in her bone marrow c. Induce involution of her thymus d. Inhibit macrophage release of IFN-γ e. Reduce plasma cell secretion of IgG antibodies

a. Decrease T-cell production of IL-2 Cyclosporine decreases T-cell production of IL-2, resulting in decreased T-cell proliferation. Cyclosporine treatment does not destroy bone marrow stem cells, nor does it induce thymic involution. Neither macrophage release of IFN-γ nor plasma cell secretion of IgG antibodies is affected by cyclosporine.

A 4-year-old male patient presents with signs and symptoms of febrile respiratory disease caused by adenovirus. Natural killer (NK) cells of this patient's immune system detect this patient's virally infected cells by? a. Decreased expression of MHC class I molecules on virally infected cells b. Decreased expression of pathogen-associated molecular patterns on infected cells c. ↑ expression of pattern recognition receptors on virally infected cells d. ↑ expression of somatically generated receptors on NK cells

a. Decreased expression of MHC class I molecules on virally infected cells Explanation: Natural killer cells will either detect the absence of MHC class I molecules or stress molecules on virus-infected cells or tumor cells. Pathogen associated molecular patterns (PAMPs) should be ↑ on foreign microbes. Pattern recognition receptors are on phagocytes and not on the microbes. Somatically generated cell-surface receptors are on B-cells or T-cells and do not interact with NK cells.

A 3-year-old boy is brought to the clinic by his mother due to a severe ear infection. She is upset because he just recovered from one about two months ago. On exam, he has multiple lesions on his face (pictured below) and walks with difficulty. On further questioning, his mother reveals that though he has learned to walk at 1 year of age he instead has not improved steadily like his older sister, but seems to have regressed. He is clumsy when walking and his trunk seems unstable. Which of the following is most likely responsible for his symptoms? a. Defective DNA repair enzymes b. Difficulty loading peptides on MHC proteins c. Inability to kill microbes d. Defective class switching e. Impaired neutrophil migration

a. Defective DNA repair enzymes His symptoms of recurrent infections, ataxia, and telangiectasias are consistent with ataxia telangiectasia with has a mutation in the ATM gene which causes defective DNA repair enzymes.

Which of the following is a correct pairing of a soluble molecule with its microbicidal action in the respiratory tract? a. Defensins damages microbial membranes b. Lysozyme increases microbial susceptibility to phagocytosis c. Fatty acids on the skin degrade microbial peptidoglycan d. Complement sequesters iron needed by pathogenic microbes

a. Defensins damages microbial membranes Explanation: Defensins can attach to microbes and create pores in the microbial membrane. Lysozyme degrades peptidoglycan; surfactant increases microbial susceptibility to phagocytosis. Fatty acids on the skin prevent microbial growth. Complement lyses bacteria, is an opsonin which facilitates phagocytosis, and is a chemokine. Transferrin and lactoferrin sequester iron needed by pathogenic microbes.

A 76-year-old male is diagnosed with Escherichia coli septicemia. The initial immune response to E. coli (gram-negative bacteria) will include? a. Detection of the E. coli lipopolysaccharide by receptors on macrophages b. Formation of specific somatically generated receptors to bind E. coli c. Generation and secretion of specific antibodies to recognize E. coli d. Production of E. coli-specific cytokines by lymphocytes e. Stimulation of killer activation receptors on NK cells

a. Detection of the E. coli lipopolysaccharide by receptors on macrophages Explanation: Initial response to gram-negative bacteria is that the lipopolysaccharide of the bacteria is recognized by a pattern recognition receptor (PRR) on a macrophage. As a result of receptor engagement, the microbes are ingested and degraded, the macrophage is activated, and cytokine production and inflammation result. Actions of somatically generated receptors of B and T cells and of antibodies are part of the adaptive immune response which occurs after the innate response. Cytokines do not have antigen-specific activities, and killer activation receptors on NK cells recognize stress-related molecules on the surfaces of abnormal host cells.

A 23-year-old woman presents to the clinic with a 6-day history of productive cough, chills, fever, and malaise. History is significant for celiac disease and recurrent sinus infections. She had hives and hypotension after receiving a blood transfusion for postpartum hemorrhage 2 years ago. Temperature is 38.9°C (102°F), and respirations are 28/min. On physical examination, breath sounds are decreased in the right lung field, and crackles are heard on auscultation. X-ray of the chest shows a new infiltrate and consolidation in the right lower lobe. This patient is at ↑ risk for infection with which of the following organisms? a. Giardia lamblia b, HIV c. Mycobacterium tuberculosis d. Neisseria meningitidis e. Strongyloides stercoralis

a. Giardia lamblia Explanation: IgA deficiency presents with recurrent pneumonia, recurrent sinusitis, an ↑ incidence of autoimmune diseases, and in a minority of patients, a risk for anaphylaxis with blood products containing IgA. Patients with IgA deficiency are at an ↑ risk for infection with Giardia due to impaired defenses in the GI tract.

A 20-month-old girl is brought to the clinic because of poor appetite and failure to gain weight. She has a history of several treated episodes of oral candidiasis. The girl's mother used injectable drugs throughout her pregnancy, did not receive prenatal care, and delivered her child at home. The child is in the fifth percentile for weight and height. Physical examination reveals diffuse lymphadenopathy. Additional testing in the office reveals moderate developmental delay. Which of the following is the most likely diagnosis? a. HIV infection b. DiGeorge syndrome c. Bruton's agammaglobulinemia d. Ataxia telangiectasia e. Wiskott-Aldrich syndrome

a. HIV infection HIV infection in a young child can present with recurrent oral candidiasis, failure to thrive, developmental delay, and/or diffuse lymphadenopathy.

Which of the following immunoglobulin is most effective at inhibiting H. pylori attachment to the stomach lining? a. IgA b. IgD c. IgE d. IgG e. IgM

a. IgA Explanation: IgA is most effective at preventing microbial attachment to mucosal membranes; it is the most abundant immunoglobulin at mucosal membrane sites. IgG is effective against neutralizing bacteria, viruses, and toxins but it is more abundant in serum.

Which of the following is the predominant immunoglobulin isotype secreted in the human mucosal associated lymphoid tissue? a. IgA b. IgD c. IgE d. IgG e. IgM

a. IgA Explanation: Most of the antibody generated in the human MALT (mucosa-associated lymphoid tissues) is of the IgA isotype. IgE, IgG, and IgM are present, but at far lower levels, and IgD is essentially absent.

Natural killer cells assess whether other cells are abnormal by detecting? a. MHC class I molecules b. Pathogen-associated molecular patterns c. Pattern recognition receptors d. Somatically generated cell-surface receptors

a. MHC class I molecules Explanation: MHC class I molecules are found on all nucleated human cells. Natural killer cells will either detect the absence of MHC class I molecules or stress molecules on virus-infected cells or tumor cells. Pathogen associated molecular patterns (PAMPs) are found on foreign microbes. Pattern recognition receptors are on phagocytes and detect PAMPs. Somatically generated cell-surface receptors are on B-cells or T-cells and do not interact with NK cells.

An 8-year-old female with a known allergy to peanuts inadvertently ingests a cereal containing traces of peanuts. Within 1 hour, she develops diffuse erythema and urticaria associated with respiratory symptoms of shortness of breath and diffuse wheezing. These findings suggest which of the following events? a. Type I hypersensitivity reaction b. Arthus reaction c. FcR-bearing cells binding to host cells coated with IgG d. IgG binding to extracellular matrix of the respiratory passages e. IgM-mediated interaction with cell membranes of lymphocytes

a. Type I hypersensitivity reaction This individual has experienced an immediate or type I hypersensitivity. The clue here is that this reaction occurred within 1 hour of antigen (peanut) ingestion. Her presentation shows hallmarks of IgE-mediated anaphylactic reactions. Arthus reactions and those mediated by IgM and IgG neither cause mast cell degranulation nor do they cause rapid respiratory distress.

A 2-year-old girl is brought to the office by her parents because of a 2-day history of ear pain evidenced by the child frequently pulling on her ears. She has a history of skin abscesses requiring incision and drainage, recurring fungal and bacterial pneumonia, and long-standing diaper rash refractory to medication. Physical examination shows oral thrush and bilateral bulging of tympanic membranes. Laboratory studies show normal leukocyte, platelet, and erythrocyte counts. The patient's neutrophils are found to have low activity of NADPH oxidase. Which of the following modes inheritance is the most likely cause of this patient's presentation? a. X-linked recessive b. X-linked dominant c. Autosomal recessive d. Autosomal dominant e. Spontaneous

a. X-linked recessive CGD is characterized by recurrent pulmonary and cutaneous infections. It is diagnosed by negative tetrazolium blue test. The most common form of CGD is inherited in an X-linked recessive manner and may manifest in females due to skewed X-chromosome inactivation of the wild-type allele.

Following a motor vehicle accident, a 25-year-old male requires a blood transfusion. Blood type tests done prior to the transfusion involve the use of IgM antibodies against A and B antigens on erythrocytes. A positive reaction is an aggregate formation that is known as? a. agglutination b. complement activation c. neutralization d. opsonization e. precipitin reaction

a. agglutination Agglutination is the aggregation or clumping of cells or particles bound together by antibodies (usually IgM or dimeric IgA). Complement activation is initiated by the attachment of the C1 component of complement to epitope-bound antibody (IgM or IgG). Neutralization is the blocking by antibody of structures on microbes and toxins that allow them to bind to host cell surfaces. Opsonization is the increased phagocytic uptake of cells or molecules tagged by antibodies (usually IgG1). The precipitin reaction results from the assembly of large antigen-antibody complexes causing them to precipitate from solution.

An 18-year-old female presents with signs and symptoms of hemolytic anemia for which most common causes are ruled out. To determine if the anemia is caused by an autoimmune reaction, which of the following approaches can be employed? a. direct coombs assay b. flow cytometry c. peripheral blood smear analysis d. complete blood count with differential

a. direct coombs assay The direct Coombs assay is used. In some autoimmune hemolytic anemias, affected individuals produce antibodies against self-blood group antigens. They will have antibodies to their own erythrocytes but in isotype or quantities that do not directly agglutinate their erythrocytes. In the direct Coombs test, autoantibodies are detected by the addition of antihuman immunoglobulin. If the patient has autoantibodies coating their red blood cells, then addition of antihuman immunoglobulin will result in clumping and a positive test result. None of the other choices of test listed can provide this type of information. A complete blood count with differential can show anemia and a peripheral blood smear analysis can show evidence of hemolysis but cannot differentiate between causes (autoimmune versus non-autoimmune). Flow cytometry looks at leukocytes, not RBCs.

A 39-year-old woman, gravida 1, para 0, at 24 weeks of gestation comes to the office with her husband, who is the biological father of the fetus. Her blood type is AB, and her husband's blood genotype is AO. Which of the following represents the probability that the unborn child in this scenario will have the AB blood type? a. 0% b. 25% c. 50% d. 100%

b. 25%

What are pathogen-associated molecular patterns (PAMPs)? a. Allow B and T lymphocytes to recognize bacteria and destroy them b. Are recognized by pattern recognition receptors of the innate immune system c. Resemble host cell surface proteins and sugars d. Contain cysteine-rich peptides that form channels in bacterial membranes e. Induce secretion of interferons by virally infected host cells

b. Are recognized by pattern recognition receptors of the innate immune system Explanation: Pattern recognition receptors of the innate immune system bind PAMPs that are found on microbes. This mechanism allows for a rapid and precise recognition of potential pathogens. In contrast, B and T lymphocytes are components of the adaptive immune system in which somatically generated receptors recognize specific antigens as opposed to broad structural characteristics found in pathogen-associated molecular patterns.

A 7-year-old girl is brought to the clinic because of an abscess on her right arm. She has had recurrent abscesses for most of her life. Physical examination reveals several small abscesses without surrounding erythema on her arm. Culture of the fluid collected during an incision and drainage procedure reveals infection with staphylococci. Laboratory studies show: Leukocyte count: 7000/mm3 Neutrophils: 54% Eosinophils: 30% Basophils: 0% Lymphocytes: 10% Monocytes: 6% IgA: 100 mg/dL IgE: 1000 mg/dL IgG: 700 mg/dL IgM: 100 mg/dL What other clinical finding is this disorder associated with? a. Telangiectasia b. Atopic dermatitis c. Albinism d. Cleft palate e. No germinal center formation

b. Atopic dermatitis Explanation: Patients with Job syndrome present with a history of recurrent staphylococcal abscesses, elevated IgE levels, and hypereosinophilia. Other findings include atopic dermatitis, coarse facies, and retained primary teeth. Ataxia telangiectasia will have ataxia, telangiectasia, and recurrent pyogenic infections but should not have eosinophilia. Albinism is seen in Chediak Higashi which present with chunky neutrophil granules. Cleft palates are seen in DiGeorge's syndrome which causes thymic aplasia and absent T-cells. Lack of germinal centers will be seen in disorders with absent B-cells.

In humans, MHC class II molecules are expressed by? a. All nucleated cells b. B-cells, dendritic cells, and macrophages c. Erythrocytes d. Platelets e. Naïve T-cells

b. B-cells, dendritic cells, and macrophages Explanation: B-cells, dendritic cells, and macrophages are the only cells that express MHC class II molecules. MHC class I molecules are expressed on all nucleated cells and platelets. Erythrocytes do not express MHC class II molecules.

Immunologic memory refers to? a. Activation of phagocytic cells to ingest microbial invaders b. Changes in adaptive immune responses with subsequent encounters with antigen c. Constancy of the response of the innate immune response to a particular microbe d. Recognition of pathogen-associated molecular patterns by pattern recognition receptors e. Stimulating a defective host cell with reduced MHC I molecules to undergo apoptosis

b. Changes in adaptive immune responses with subsequent encounters with antigen Explanation: A hallmark of the adaptive immune system is that it progressively alters its response upon reexposure to an antigenic stimulus, and in doing so, it must recall the previous exposure, a process known as memory. Although they are members of the innate immune system and do not possess immunologic memory, phagocytes may be influenced by the adaptive immune system. Consistency in immune response from initial to subsequent encounters is a hallmark of the innate immune response. Immunologic memory of the adaptive immune system is not passed genetically from one generation of individuals to the next. Detection of diminished MHC class I expression is a function of natural killer cells, members of the innate immune system.

With no therapeutic intervention, the most likely outcome for a transplanted skin graft obtained from an unrelated donor who is HLA identical to the recipient is? a. Acute rejection b. Chronic rejection c. Graft-versus-host disease d. Hyperacute rejection e. Long-term success

b. Chronic rejection Chronic rejection is most likely to occur, over months to years, in such a situation. Unrelated HLA identical individuals will have numerous mismatches of minor histocompatibility genes. Because the major histocompatibility genes match, hyperacute and acute rejections are unlikely to occur. Skin does not contain immunocompetent tissue and cannot mount a graft versus host response. Even with identical major histocompatibility genes, long-term success of a transplanted skin graft will require immunosuppressive therapy.

A 22-year-old woman reports of increasing fatigue and pale appearance. She reports that her urine appears brown each morning. Laboratory studies show a hemoglobin of 10 g/dL. Which of the following best describes the most likely mechanism of erythrocyte injury in this condition? a. Point mutation in the LYST gene b. Complement-mediated hemolysis c. ↑ oxidative injury by H2O2 due to decreased NADPH d. Phagocytosis of RBCs due to complement fixation e. Phagocytosis of RBCs, which have surface-bound Igs

b. Complement-mediated hemolysis Explanation: PNH is an acquired clonal stem cell disorder characterized by intravascular hemolysis with anemia and "cola-colored" urine in the morning. The mild respiratory acidosis that occurs during sleep activates complement and lyses RBCs because glycosylphosphatidylinositol (GPI) is defective and cannot bind CD55 and CD59 and protect the RBCs from complement-mediated lysis.

Lymphoid cells? a. Are the most numerous leukocyte population b. Consist of B, T, and NK cells c. Contain cytoplasmic granules d. Phagocytize debris and foreign cells

b. Consist of B, T, and NK cells Explanation: Lymphocytes include B cells, T-cells, and natural killer (NK) cells. They account for fewer than 40% of blood leukocytes; neutrophils are the most numerous. Lymphoid lineage cells are agranulocytes without cytoplasmic granules and are not phagocytic.

Immune recognition of molecules belonging to "self" is important to? a. Activate natural killer cells b. Determine the safety of interacting w/the molecule c. Induce somatic recombination of B-cell and T-cell receptors d. Stimulate binding by pattern recognition receptors e. Trigger an attack on the cell expressing the self molecule

b. Determine the safety of interacting w/the molecule Explanation: Identification of self tells the immune system that the cell or molecule recognized is not foreign and safe to interact with. On the contrary, pattern recognition receptors are genetically programmed to recognize non-self. Triggering an attack on a cell expressing the "self" molecule leads to autoimmune diseases.

A female neonate has a malformed jaw, cardiac abnormalities, and hypocalcemia, in addition to diminished cell-mediated and B-cell responses. Which of the following immune deficiencies should be included in the differential diagnosis of this patient? a. Adenosine deaminase (ADA) deficiency b. DiGeorge syndrome c. Hereditary angioedema d. Severe combine immunodeficiency disease (SCID) e. Wiskott-Aldrich syndrome

b. DiGeorge syndrome Explanation: The defects in jaw and cardiac structure and the defective calcium metabolism (because of abnormal parathyroid development) point to aberrant development of structures derived from the third and fourth pharyngeal pouches. None of the other diseases given are associated with these accompanying features. This individual is likely to also include the thymus, and this patient is likely to have an underdeveloped thymus, which is a hallmark of DiGeorge syndrome.

A female neonate has a malformed jaw, cardiac abnormalities, and hypocalcemia, in addition to diminished cell-mediated and B-cell responses. Which of the following immune deficiencies should be included in the differential diagnosis of this patient? a. Adenosine deaminase deficiency b. DiGeorge syndrome c. Bruton's agammaglobulinemia d. Severe combine immunodeficiency disease e. Wiskott-Aldrich syndrome

b. DiGeorge syndrome The defects in jaw and cardiac structure and the defective calcium metabolism (because of abnormal parathyroid development) point to aberrant development of structures derived from the third and fourth pharyngeal pouches. None of the other diseases given are associated with these accompanying features. This individual is likely to also include the thymus, and this patient is likely to have an underdeveloped thymus, which is a hallmark of DiGeorge syndrome.

A 23-year-old female has HLA genotype A3/A8, B1/B8, C4/C1. For each locus, the maternal allele is listed first and the paternal allele second. Several potential donors are available for an organ graft. Which of the following donors would be the closest match? a. Donor A: A8/A27, B24/B8, C4/C9 b. Donor B: A3/A3, B27/B8, C1/C1 c. Donor C: A8/A6, B44/B8, C4/C1 d. Donor D: A6/A27, B1/B8, C4/C2 e. Donor E: A3/A8, B1/B27, C9/C4

b. Donor B: A3/A3, B27/B8, C1/C1 The closest match will have the fewest mismatched HLA genes not present in the recipient. For donor B, only HLA B27 is not already present in the recipient. Donor A has three mismatches, Donor C has two mismatches, Donor D has three mismatches, and Donor E has two mismatches.

Which of the following types of cells are notable for their presence at the sites of helminth infections? a. Basophils b. Eosinophils c. Lymphocytes d. Monocytes e. Neutrophils

b. Eosinophils Explanation: Eosinophils contain IgE receptors for mutation towards parasites (including helminths).

A 55-year-old male comes to the clinic with fever and abdominal fullness. His temperature is 39.1°C (102.3°F). Physical examination shows hepatosplenomegaly and lymphadenopathy. Laboratory studies show anemia, thrombocytopenia, hypertriglyceridemia, elevated transaminases, and a very high ferritin. Which of the following is the most likely cause of this patient's condition? a. Defective NADPH oxidase b. Excess cytokine release by macrophages c. Failed repair of double-stranded breaks in DNA d. Impaired leukocyte migration and adhesion to the vascular endothelium e. Microtubule dysfunction with failure of phagosome-lysosome fusion

b. Excess cytokine release by macrophages Explanation: HLH may present with fever, hepatosplenomegaly, and lymphadenopathy, with anemia, thrombocytopenia, hypertriglyceridemia, and high inflammatory markers. HLH is caused by hyperinflammation and proliferation of macrophages that secrete cytokines and improperly phagocytize host blood cells.

Which of the following describes commensal microbes? a. Exist only in the gastrointestinal tract b. Exist in a symbiotic relationship with the body c. Produce toxins that cross the epithelium d. Provide nutrients for pathogens e. Induce inflammation under homeostatic conditions

b. Exist in a symbiotic relationship with the body Explanation: Commensal microbes are those that exist in a symbiotic relationship with the body. Commensal microbes colonizing many locations in the body including the skin and gastrointestinal tracts inhibit the establishment of other potentially pathogenic microbes by utilizing nutrients that are required for pathogen growth and toxicity.

What is the function of the classical pathway of complement? a. Cleave immunoglobulins into Fc fragments b. Facilitate destruction of microbes c. Recognize specific epitopes on microbes d. Regulate lymphocyte development e. Trigger histamine release

b. Facilitate destruction of microbes Explanation: Complement functions to facilitate the lysis of microbes, opsonization of microbes, and release of C3a and C5a which function as chemokines. Immunoglobulin molecules are not cleaved by complement. The classical pathway is activated only by antigen-antibody complexes and by itself does not recognize microbial epitopes. Complement is not involved in lymphocyte development and does not trigger the release of histamine.

Antibody-mediated recruitment of macrophages occurs through action of? a. Complement receptors b. Fc receptors c. Killer activation receptors d. Pattern recognition receptors e. Toll-like receptors

b. Fc receptors Explanation: Binding to an epitope causes a conformation change in the Fc portion of the antibody molecule. Fc receptors (FcRs) recognize and bind to the conformationally altered antibody molecule, and this engagement of epitope-bound antibody by FcRs stimulates phagocytosis of cells and molecules "tagged" by antibodies for destruction. Complement receptors bind and facilitate the phagocytosis of cells and molecules tagged by complement components or fragments. Killer activation receptors, pattern recognition receptors, and toll-like receptors do not recognize antigen-antibody complexes.

Receptors found on B and T lymphocytes are? a. Encoded in the germline DNA b. Generated via somatic recombination c. Produced rapidly after an initial encounter with non-self d. Recognize shared microbial patterns

b. Generated via somatic recombination Explanation: B-cells and T-cells receptors are somatically generated during development and are not present in the germline DNA. They are specific and take days to weeks to generate. The innate immune receptors are encoded in the germine DNA and recognize shared microbial patterns.

A 34-year-old female presents with 2 months of fever, night sweats, diarrhea, and weight loss. She was a relatively healthy child. Temperature is 39.1°C (102.4°F), heart rate is 94/min, respirations are 18/min, and blood pressure is 136/92 mm Hg. Physical examination shows muscle wasting and chest x-ray shows bilateral lung infiltrates. Laboratory studies show a a CD4+ count of less than 50 cells/mm³. Which of the following diseases is the best underlying cause of this patient's most likely condition? a. Omenn syndrome b. HIV/AIDS c. DiGeorge syndrome d. Bare lymphocyte syndrome e. Severe combined immunodeficiency

b. HIV/AIDS Disseminated M. avium complex infection occurs in the setting of uncontrolled HIV and a CD4+ cell count of less than 50/mm3. While the other answers are not wrong in terms of this patient's symptoms, B is the best answer because HIV can be acquired and this is not likely to be congenital given that the history stated that she was a relatively healthy child.

A 62-year-old female is brought to the emergency department because of daily fevers and diarrhea for the past 3 weeks. She has also had a 1.2-kg (2.6-lb) weight loss. Physical examination reveals pallor, hepatomegaly, and splenomegaly. Laboratory studies show: White blood cells: 1.2 × 103/µL Hemoglobin: 7.4 g/dL Hematocrit: 23% Platelets: 109,000/µL Ferritin: 8000 mcg/L Findings on histopathologic examination of bone marrow aspirate are shown. What is the most likely diagnosis? a. Chediak-Higaski syndrome b. Hemophagocytic lymphohistiocytosis c. Multiple myeloma d. Acute leukemia

b. Hemophagocytic lymphohistiocytosis Explanation: HLH often presents with fever, splenomegaly, cytopenias, hypertriglyceridemia, and hemophagocytosis in the bone marrow. HLH is a disease of immune system overactivation that can be inherited due to autosomal recessive mutations in several genes or may occur secondary to infection (particularly with Epstein-Barr virus), malignancy, or rheumatologic disorders.

A 7 year old child has a peanut allergy with symptoms that include generalized itching and hives after eating peanuts. For this child, a peanut is most likely an a. Superantigen b. Immunogen c. Tolerogen d. Pathogen-associated molecular patterns (PAMPs)

b. Immunogen Explanation: An immunogen is molecule or substance that stimulates an immune response; in this child, the peanut is stimulating an immune reaction. A superantigen is a molecule that elicits T-cell responses and bypasses the need for costimulatory molecules; these are usually potent bacterial antigens like staphylococcal enterotoxin or toxic shock syndrome toxin. A tolerogen diminishes the immune response so if the peanut were a tolerogen, the child should be asymptomatic. Pathogen-associated molecular patterns (PAMPs) are on microbes and a peanut is not a microbe.

During a hospital stay, a catheter was placed into the urethra of a 70-year-old male who subsequently developed a urinary tract infection. Which was one of the factors that most likely contributed to the establishment of the infection? a. ↑ urinary flow b. Introduction of microbes into the urethra during placement of the catheter c. Mucus secretion from epithelial cells lining the urinary tract d. pH levels in the sterile urine of the catheterized patient

b. Introduction of microbes into the urethra during placement of the catheter Explanation: Placement of a catheter into the urethra can facilitate access of microbes from the external surface. The catheter does not itself alter urinary pH or mucus production. ↑ urinary flow should flush potential microbes out of the host system.

A 3-year-old boy is admitted to the hospital with Aspergillus pneumonia. Immunodeficiency evaluation reveals a mutation in the NADPH oxidase. Which of the following clinical findings are most typical in patients with this mutation? a. Abnormal facies, congenital heart defects, and hypoparathyroidism b. Lymphadenitis, liver abscess, and granulomas in the gastrointestinal and urinary tract c. Periodontitis, easy bruising, and albinism d. Recurrent infections, eczema, and small platelets e. Retained primary teeth, coarse facies, and eczema

b. Lymphadenitis, liver abscess, and granulomas in the gastrointestinal and urinary tract CGD is caused by a mutation in the genes coding for the subunits of the NADPH oxidase complex. Patients with CGD usually present with recurrent pneumonia, lymphadenitis, liver abscess, skin abscess, and granulomas involving the gastrointestinal and urinary tract. Option A is DiGeorge syndrome, C is Chediak Higashi, D is Wiskott-Aldrich syndrome, and E is Job syndrome.

Natural killer cells are members of which of the following families of leukocytes? a. Myelocytes b. Lymphocytes c. Phagocytes d. Antigen presenting cells e. Granulocytes

b. Lymphocytes Explanation: Natural killer (NK) cells are lymphocytes, which also include B-cells and T-cells. Myelocytes include neutrophils, eosinophils, basophils, mast cells, monocytes, macrophages, and dendritic cells. Granulocytes are myelocytes with granules and include neutrophils, eosinophils, basophils, and mast cells. Phagocytes are neutrophils, macrophages, monocytes, and dendritic cells. Antigen presenting cells are macrophages, dendritic cells, and B-cells.

4-year-old boy is brought to the emergency department for knee pain and swelling. He has a history of easy bruising and recurrent skin and respiratory infections. Temperature is 38.3°C (101°F). On physical examination, his right knee is warm and tender on palpation. He has very fair skin, white hair, and light-colored irises. Which of the following mechanisms best characterizes this patient's most likely diagnosis? a. Defective NADPH oxidase b. Microtubule dysfunction c. Mutation of the X chromosome d. Defective integrin adhesion protein e. Mutated perforin

b. Microtubule dysfunction Explanation: Symptoms of Chédiak-Higashi syndrome include albinism, recurrent infections, peripheral neuropathy, and bleeding tendencies such as easy bruising. Chédiak-Higashi syndrome is caused by microtubule dysfunction resulting in abnormal cellular trafficking and failure of phagolysosome formation. It is inherited in an autosomal recessive manner.

A 19-year-old male sustained a skin laceration and became ill with a fever, general muscle aches, and dizziness; then he lost consciousness. On arrival in the emergency department, he had a temperature of 102.2°F and a heart rate of 136 beats per minute. His complete blood count was 22,000 cells per μL (Reference range: 4,500 to 12,500 per μl). The predominant cell type in this patient's blood is most likely? a. B lymphocytes b. Neutrophils c. Monocytes d. Natural killer cells e. T lymphocytes

b. Neutrophils Explanation: Neutrophils are quickly ↑ during an acute infection and are the most abundant white blood cell.

A 12-hour-old male newborn is evaluated for jaundice, abdominal swelling, and difficulty breathing. He was born at term to a G2P2 woman. The pregnancy and delivery were uneventful. Lab testing shows that both mother and infant are ABO group O. Mixing the infant and maternal blood in vitro causes agglutination. Which of the following most likely contributes to this infant's disease? a. newborn is Rh-negative b. Rh-negative mother had a prior pregnancy with a Rh-positive fetus c. mother is Rh positive d. mother is at risk for hemolytic anemia due to fetal antibodies e. mother's child from previous pregnancy is Rh negative

b. Rh-negative mother had a prior pregnancy with a Rh-positive fetus Erythroblastosis fetalis is an autoimmune hemolytic anemia that is most likely caused by Rh incompatibility and may present with jaundice, hepatosplenomegaly, and respiratory distress. When the mother had her first child, she was likely Rh negative and the child was Rh positive, resulting in the formation of maternal IgG antibodies that can affect future pregnancies.

An 84-year-old man is admitted to the hospital for a 2-day history of bloody diarrhea. He is hemodynamically stable, but testing reveals a hemoglobin of 8.0 g/dL. An RBC transfusion is ordered. Soon after the transfusion begins, the patient complains of nausea and flank and chest pain. Vitals show a temperature of 103°F (39.4°C), pulse 125/min, respirations are 20/min, and blood pressure 95/65 mm Hg. After stopping the transfusion, it is noted that the RBC unit that was being administered is blood type AB negative, and the patient's blood type is A positive. Which type of hypersensitivity reaction is responsible for this patient's posttransfusion signs and symptoms? a. Type I b. Type II c. Type III d. Type IV

b. Type II ABO-incompatible red cell transfusions cause acute hemolytic transfusion reactions, which present with fever, flank pain, and circulatory collapse. The underlying mechanism of acute hemolytic transfusion is a type II hypersensitivity reaction in which IgG antibodies bind to donor RBCs, leading to complement-mediated hemolysis.

A 28-year-old female presented with an acute urinary tract infection and is given amoxicillin. Her symptoms resolved, and she completed the course of antibiotic therapy. Two weeks later, she presented with fatigue, dyspnea (difficulty in breathing), and tachycardia (rapid heart rate). Autoimmune hemolytic anemia is diagnosed based on decreased hemoglobin and a positive direct Coombs test (presence of antibodies on erythrocyte surfaces). These findings suggest which type of hypersensitivity? a. Type I, mediated by CD4+ T-cells b. Type II, mediated by IgG antibodies c. Type III, mediated by IgM antibodies d. Type IV, mediated by CD4+ T-cells e. Type IV, mediated by IgE antibodies

b. Type II, mediated by IgG antibodies Autoimmune hemolytic anemia is caused by IgG antibodies in a type II hypersensitivity reaction.

A 35-year-old male presents with headache, fatigue, light-headedness, dyspnea, and tachycardia. Laboratory findings reveal decreased hemoglobin and a positive direct Coombs test (presence of antibodies on erythrocyte surfaces). The patient is currently taking an antibiotic for symptoms of upper respiratory infection. These findings suggest which type of hypersensitivity? a. Type I, mediated by IgG antibodies b. Type II, mediated by IgG antibodies c. Type III, mediated by IgG antibodies d. Type III, mediated by IgG or IgM antibodies e. Type IV, mediated by CD4+ T-cells

b. Type II, mediated by IgG antibodies Type II reactions involve antibodies directed against self-cells (such as erythrocytes) or membranes. Certain drugs react with erythrocytes to form neoantigens. Type I responses are against foreign antigens (e.g., allergens), cause IgE responses, and do not invoke a Coombs reaction. Type III reactions involve soluble antigen-antibody complexes, and type IV reactions do not involve antibody.

A 1-year-old boy is brought to the emergency room for bloody diarrhea. He has a history of recurrent ear infections, diarrhea, and atopic dermatitis. He had an older sibling who died of a pulmonary infection at a young age. On physical exam, there is dried blood in his nares bilaterally and bleeding at intravenous puncture sites. Additionally, purpura is noted on his arms. Laboratory results show marked thrombocytopenia requiring platelet transfusions. A peripheral smear shows decreased platelets that are predominantly small. Immunoglobulin levels show decreased IgG and IgE but increased IgM and IgA. What gene is likely mutated in this patient? a. STAT3 b. WASP c. ATM d. BTK e. PIGA

b. WASP The patient's symptoms of immunodeficiency and thrombocytopenia are consistent with Wiskott-Aldrich syndrome which is due to a WASP mutation. Peripheral smear has microthombocytopenia. STAT3 is seen in Job syndrome which has increased IgE. ATM will typically present with ataxia and telangiectasia. BTK is seen in Bruton's tyrosine kinase deficiency resulting in complete agammaglobulinemia. PIGA gene is seen in paroxysmal nocturnal hemoglobinuria which would have increased schistocytes on peripheral smear.

A multigravid woman who is Rh-negative gives birth to a male neonate who is in distress and is evaluated in the labor and delivery suite. On examination, he is pale and has a yellow-colored umbilical cord, skin, and eyes. His abdomen is distended with hepatosplenomegaly and generalized body wall edema. Laboratory results are as follows: Hematocrit: 24% Hemoglobin: 4.9 g/dL Reticulocyte count: 24% Serum lactate dehydrogenase: 4500 units/L Blood group: B Rh+ Which of the following mechanisms best explains this neonate's most likely diagnosis? a. Anti-Rh IgG given to mother hemolyzed fetal erythrocytes b. fetal erythrocytes from previous pregnancy sensitized mother against Rh antigen c. maternal erythrocytes sensitized fetus to maternal B antigen d. maternal leukocytes destroyed fetal erythrocytes e. fetus produced autoantibodies against his own erythrocytes

b. fetal erythrocytes from previous pregnancy sensitized mother against Rh antigen HDFN may cause hyperbilirubinemia, along with hydrops fetalis. HDFN most commonly occurs due to maternal alloimmunization/sensitization against Rh(D) antigen from previous pregnancy.

Which of the following is a potential outcome of a self-reactive CD4+ T-cell that receives constant stimulation through the TCR without costimulation? a. Proliferation b. Differentiation into a Tfh cell c. Anergy d. Development to a memory T-cell e. Production of high amounts of IL-2

c. Anergy Explanation: Anergy is a state of nonreactivity that occurs when a lymphocyte receives a stimulus through its TCR or BCR in the absence of the additional appropriate signals provides by antigen-presenting cells or T-cells. Constant stimulation of the TCR on self-reactive T-cells in the periphery without secondary costimulation typically results in anergy and/or potentially apoptosis. When T-cells receive stimulation through both the TCR and costimulatory molecules, the T-cells produce IL-2, proliferate and differentiate into either effector T-cells or memory T-cells.

A 34-year-old female with an autoimmune disorder is found to have B-cells that react very strongly to her own self-antigens. The process that is likely defective is called? a. Positive selection b. Antigen dependent clonal selection c. Anergy d. Isotype switching e. T-cell independent activation

c. Anergy Explanation: Anergy occurs when B-cell activation and antibody production are turned off to prevent autoreactivity for self-tolerance. Without anergy, individuals will have a high susceptibility to autoimmune disorders. Antigen dependent clonal selection or B-cell activation, T-cell independent activation, and isotype switching occurs after positive selection and negative selection but do not contribute to autoimmunity.

A 6-month-old male infant has diarrhea, extensive fungal infections, and skin rashes and has failed to gain weight. He is deficient in both T and B-cell function. The thymus is of normal size. The most common cause of the patient's symptoms is inherited as what type of disorder? a. Mitochondrial b. X-linked dominant c. Autosomal recessive d. Autosomal dominant e. Spontaneous

c. Autosomal recessive Patients with SCID usually present with recurrent infections, opportunistic infections, infections that are difficult to treat, failure to thrive, and lack of lymph tissues on the physical exam. The T-cells and B-cells are always absent or very low. The most common cause is adenosine deaminase deficiency (autosomal recessive) or IL-2 receptor mutation (X-linked recessive).

Which of the following cells have been implicated in the prevention of autoimmune disorders? a. Antigen-presenting cells b. Anergized T-cells c. CD4+CD25+ Treg cells d. Follicular Th cells e. Naïve T-cells

c. CD4+CD25+ Treg cells Explanation: CD4+CD25+ Treg cells inhibit various responses against self epitopes as well as some responses against epitopes associated with infectious agents and tumors. Antigen-presenting cells do not have this capacity. Anergized cells are inactive. Follicular dendritic cells are involved in the display of antigen to B-cells and T-cells in the lymph node follicles. Naïve T-cells require activation before they can begin to carry out any of their effector functions.

An 8-month-old female patient is evaluated for recurrent bacterial infections. Examination reveals albinism of the eyes and skin. Testing reveals decreased NK and T-cell functions, and further evaluation reveals impaired fusion of lysosomes with phagosomes. The disorder most likely to be responsible for the findings in this patient is? a. Adenosine deaminase deficiency b. Bruton's agammaglobulinemia c. Chediak-Higashi syndrome d. Severe combined immune deficiency e. Congenital HIV/AIDS

c. Chediak-Higashi syndrome Chediak-Higashi syndrome is caused by an inability to fuse lysosomes with phagosomes and affects phagocytes and natural killer cells. Chédiak-Higashi syndrome is an immunodeficiency that presents with impaired phagocytosis, partial albinism, and platelet defects due to a defect in microtubule polymerization.

A 45-year-old female presents with recurrent sinusitis requiring antibiotic treatment. She has had several hospitalizations recently for bacterial pneumonia. She also reports symptoms of chronic diarrhea. Serum immunoglobulin assessments reveal a significantly decreased level of IgG and a mildly decreased level of IgA. Based on these findings, the most likely underlying process is? a. Chediak-Higashi syndrome b. Chronic granulomatous disease c. Common variable immunoglobulin deficiency d. Hyper IgE syndrome e. DiGeorge syndrome

c. Common variable immunoglobulin deficiency This patient has signs and symptoms consistent of common variable immunoglobulin deficiency with nonspecific findings and defects in both B-cell and T-cells.

A previously healthy 8-month-old female with fever and wheezing is diagnosed with respiratory syncytial virus (RSV) infection. Assuming that this is the child's first exposure to RSV, which of the following mechanisms will most likely operate to clear the infection? a. CD4+ T-cell-mediated necrosis of infected cells b. Complement-mediated lysis of infected cells c. Cytotoxic T-cell-induced apoptosis of infected cells d. MHC II presentation of viral peptides on CD8+ T-cells e. Virus-specific antibodies that neutralize free virus

c. Cytotoxic T-cell-induced apoptosis of infected cells Explanation: Clearance of viral infections involves destruction of infected cells by cytotoxic T-cells to prevent viral replication. CD4+ T-cell responses against infected cells are typically effective when the infectious agent is residing within intracellular endosomes. Complement is not effective against intracellular microbes, and sufficient levels of antibodies against the microbes are usually not yet present during primary infections. MHC presentation of viral peptides occurs on APCs, not on CD8+ T-cells.

A 2-year-old boy is brought to the pediatrician's office by his parents because of a fever and cough for the past 3 days. He has a history of frequent ear infections, chronic diarrhea, and multiple hospitalizations for pneumonia. He is up to date with his vaccinations. X-ray of the chest demonstrates diffuse, bilateral interstitial infiltrates. A bronchoalveolar lavage sample shows Pneumocystis jirovecii. An immunoglobulin panel shows an IgA level of 62 mg/dL, IgM level of 380 mg/dL, and IgG level of 48.3 mg/dL. Which of the following best describes the mechanism responsible for this patient's condition? a. Defect in B-cell maturation b. Defect in reduced NAPDH oxidase in neutrophils c. Defective class switching d. STAT3 mutation e. Defective leukocyte function-associated antigen-1 integrin on phagocytes

c. Defective class switching Explanation: Hyper-IgM syndrome causes immunodeficiency leading to sinopulmonary and opportunistic infections. Hyper-IgM syndrome is most commonly due to an X-linked recessive defect in CD40L on T-helper cells that results in inability to undergo isotype or class switching.

Which of the following naïve cells load peptide fragments into MHC class II molecules? a. CD4+ T cells b. CD8+ T cells c. Dendritic cells d. Neutrophils e. Plasma cells

c. Dendritic cells Explanation: Of those cell types listed, only dendritic cells can process peptide fragments and load them on MHC class II molecules for presentation. Plasma cells and lymphocytes, whether of the CD4+ or CD8+, cannot do this. Neutrophils can ingest peptides and degrade them but do not synthesize MHC class II molecules. Although not listed, please remember that B-cells can also load peptides on MHC class II molecules for presentation to Tfh cells.

A 5-year-old female has a small deletion in chromosome 22. She has impaired thymus development with a significant deficiency in the number of functional T-cells. The most likely etiology for these findings is? a. Bare lymphocyte syndrome b. Chediak-Higashi syndrome c. DiGeorge syndrome d. Job syndrome e. Chronic mucocutaneous candidiasis

c. DiGeorge syndrome Impaired thymic development leading to T-cell dysfunction and small deletions in chromosome 22 are characteristic of DiGeorge syndrome. Thymic development is normal in all of the other choices.

A 5-year-old female has no thymic shadow on x-ray with multiple fungal infections especially with Pneumocystis pneumonia and oral thrush. The most likely etiology for these findings is? a. Adenosine deaminase deficiency b. Chediak-Higashi syndrome c. DiGeorge syndrome d. Ataxia telangiectasia e. Severe combined immunodeficiency (SCID)

c. DiGeorge syndrome Impaired thymic development leading to T-cell dysfunction are characteristic of DiGeorge syndrome. Thymic development is normal in all of the other choices.

A 56-year-old man visits his primary care physician with a 4-day history of fatigue and painless dark urine. Laboratory studies show a hemoglobin of 8.2 g/dL, a mean corpuscular volume of 82 fL, and a platelet count of: 134,500/mm3. Flow cytometry reveals a population of cells that are negative for CD55 and CD59. Which of the following laboratory abnormalities is most likely in this patient? a. ↑ C5-9 b. Elevated haptoglobin c. Elevated urine hemosiderin d. ↑ white blood cell count e. ↑ hemoglobin

c. Elevated urine hemosiderin Explanation: PNH is a rare, acquired disorder caused by PIG-A GPI anchor mutation, which leads to complement-mediated intravascular hemolysis. Elevated hemosiderin will be seen on urinalysis in PNH. C5-9 does not play a role in this disease entity. Haptoglobin and hemoglobin is decreased in hemolysis. PNH can cause lysis of all lineages including WBCs, RBCs, and platelets, resulting in pancytopenia.

In an individual with an allergy to dust mites, cross-linking of which of the following molecules will trigger an inflammatory mediator release? a. Histamine b. IgA c. IgE d. IgG e. Mast cells

c. IgE Cross-linking of IgE bound to the surfaces of basophils and mast cells causes cellular degranulation and release of vasoactive amine responsible for inflammation. In humans, neither IgA nor IgG is associated with allergic responses. Histamine is released from mast cells as a result of cross-linking of surface-bound IgE.

A previously healthy 45-year-old male presents with rhinorrhea, nasal congestion, and persistent respiratory symptoms several months after returning to his home in New Orleans after Hurricane Katrina. He has noticed mold growing along the walls of his house. Skin testing for sensitivity to common mold spores gave positive results to several of them in less than 30 minutes. These findings indicate an example of? a. Contact dermatitis b. Delayed-type hypersensitivity c. Immediate hypersensitivity d. Serum sickness e. Type II hypersensitivity

c. Immediate hypersensitivity Type I (immediate) hypersensitivity is caused by the cross-linking of FcR (also known as CD23)-bound IgE antibodies on cell surfaces, which triggers the release of vasoreactive amines from mast cell granules. Antigens (allergens) are often airborne and elicit type I reactions that cause respiratory distress. Neither contact dermatitis nor delayed (-type) hypersensitivity reactions involve antibody. Both serum sickness and type II hypersensitivity involve immune complexes.

A 2-year-old boy is brought to the emergency department because of vomiting and diarrhea. Medical history is significant for six prior hospitalizations involving pneumonia, sepsis, diarrhea, and respiratory syncytial virus infection. The physical examination reveals no palpable lymph nodes. Laboratory testing shows absent T-cells, absent B-cells, and absent natural killer cells. IgA, IgE, IgG, and IgM levels are low. A defect or absence of which of the following is most likely responsible for this child's presentation? a. Bruton's tyrosine kinase b. CD40 ligand c. Interleukin-2 receptor d. Integrins e. NADPH oxidase

c. Interleukin-2 receptor Patients with SCID usually present with recurrent infections, opportunistic infections, infections that are difficult to treat, failure to thrive, and lack of lymph tissues on the physical exam. The T-cells and B-cells are always absent or very low.

The constant regions of the five major types of heavy chains of immunoglobulin molecules dictate the molecule's? a. Epitope b. Fab fragment c. Isotype d. Expression of kappa or lambda

c. Isotype Explanation: The heavy chain constant regions determine immunoglobulin isotypes: mu (μ, IgM), delta (δ, IgD), gamma (γ, IgG), epsilon (ε, IgE), and alpha (α, IgA). Fab fragments are enzymatic cleavage products of immunoglobulin monomers. Kappa or lambda expression is determined by the light chain constant region.

In a patient who later developed an allergy to a certain antigen, the initial response to the antigen consisted of immunoglobulin of the IgM class. However, over time, antigen-specific IgE came to be predominant. This change from an IgM to an IgE response is caused by? a. Affinity maturation b. Allelic exclusion c. Isotype switching d. Junctional diversity e. Somatic hypermutation

c. Isotype switching Explanation: Isotype switching is a process in which rearranged VDJ genes within a memory B cell become juxtaposed through DNA excision from an upstream (5′) C region gene with a different C region gene farther downstream (3′). Affinity maturation of antibody for its epitope is independent of isotype. For B cells that have "selected" their maternal or paternal immunoglobulin variable region genes, there are no "do-overs." Both junctional diversity and somatic hypermutation involve the antigen-binding site for immunoglobulin and do not appear to influence a switch from one isotype to another.

The binding of antibodies to microbial epitopes or soluble molecules in a manner that inhibits the ability of these microbes to bind to host cell surfaces is termed what? a. Agglutination b. Complement activation c. Neutralization d. Opsonization e. Precipitin reaction

c. Neutralization Explanation: Neutralization is the blocking by antibody of structures on microbes and toxins that allow them to bind to host cell surfaces. Agglutination is the aggregation or clumping of cells or particles bound together by antibodies (usually IgM or dimeric IgA). Complement activation is initiated by the attachment of the C1 component of complement to epitope bound antibody (IgM or IgG). Opsonization is the ↑ phagocytic uptake of cells or molecules tagged by antibodies (usually IgG1) or membrane-bound C3b or C4b. The precipitin reaction results from the assembly of large antigen-antibody complexes that precipitate from solution.

A 10-year-old boy is brought to his pediatrician for a follow-up examination. He has a history of chronic recurrent infections, including multiple episodes of pneumonia and skin abscesses. Prior infections have cultured Staphylococcus aureus, Nocardia, Aspergillus, Pseudomonas, and Serratia marcescens. Physical examination is unremarkable. Which of the following immune components is most likely abnormal in this child? a. B-cells b. Lysosomes c. Neutrophils d. Macrophages e. T-cells

c. Neutrophils Explanation: Patients with CGD often present with skin abscesses and infection with catalase-positive organisms like Aspergillus, Staphylococcus aureus, and Serratia marcescens. CGD is a disorder of neutrophils caused by a defect in NADPH oxidase which leads to inability to generate an oxidative burst (free radicals) to kill microbes.

A 67-year-old female developed pseudomembranous colitis after receiving antibiotic therapy. One possible explanation for colitis is antibiotic-induced reduction of which of the following in the colon? a. Lysozyme secretion b. Mucus secretion c. Normal commensal bacteria d. pH e. RNases and DNases

c. Normal commensal bacteria Explanation: Use of antibiotics can reduce normal commensal microbe populations, increasing the opportunity for colonization by more pathogenic microbes. The pathophysiology of pseudomembranous colitis, severe inflammation of the inner lining of the bowel, is not associated with changes in lysozyme secretion, mucus secretion, pH, or RNases and DNases.

Which of the following structures on viruses allow them to be recognized by the human immune system? a. MHC I molecules b. MHC II molecules c. Pathogen-associated molecular patterns d. Pattern recognition receptors e. Somatically generated receptors

c. Pathogen-associated molecular patterns Explanation: Viruses contain pathogen-associated molecular patterns that are recognized by pattern recognition receptors (PRRs). The pattern recognition receptors are found on host phagocytes. MHC I and II molecules are present on nucleated host cells but not on viruses. The somatically generated receptors are on B-cells and T-cells.

CD4+ T-cells that respond to intracellular pathogens by recruiting and activating phagocytic cells are termed? a. Cytotoxic T lymphocytes b. Tfh cells c. Th1 cells d. Th2 cells e. Th17 cells

c. Th1 cells Explanation: CD4+ Th1 cells recruit and activate macrophages to destroy intracellular pathogens. Cytotoxic T lymphocytes are CD8+. Tfh, Th2, and Th17 cells, although also being CD4+, do not engage in this activity.

A 45-year-old female with a history of hepatitis C viral infection presents with decreased renal function, hypertension, and anemia. Laboratory findings reveal decreased serum C3. Her urine sediment contains leukocytes, erythrocytes, and red blood cell casts (a proteinaceous mold of the renal tubules that includes erythrocytes). Her renal biopsy is consistent with glomerulonephritis. These findings suggest which type of hypersensitivity? a. Type I, mediated by CD4+ T-cells b. Type II, mediated by IgA antibodies c. Type III, mediated by IgG antibodies d. Type IV, mediated by CD4+ T-cells e. Type IV, mediated by IgG (and sometimes IgM) antibodies

c. Type III, mediated by IgG antibodies Glomerulonephritis is often associated with immune complex deposition, a type III hypersensitivity. Red blood cell casts are indicative of glomerulonephritis, and reduced C3 levels indicate a high level of cleavage and activation of C3. Type I hypersensitivity is mediated by IgE, not by CD4+ T-cells. Type II hypersensitivity responses usually involve IgG. Type IV hypersensitivities do not involve antibodies.

A 40-year-old female presents with fatigue, weight loss, arthritis of her hands, and a malar rash. Blood tests reveal the presence of antinuclear antibodies and anti-double-stranded DNA antibodies. Her symptoms and blood tests are consistent with systemic lupus erythematosus. These findings suggest which type of hypersensitivity in this patient? a. Type I, mediated by CD4+ T-cells b. Type II, mediated by IgM antibodies c. Type III, mediated by IgG antibodies and complement d. Type IV, mediated by CD4+ T-cells e. Type IV, mediated by IgG (and sometimes IgM) antibodies

c. Type III, mediated by IgG antibodies and complement Systemic lupus erythematosus results from the generation of autoimmune antibodies against chromosomal proteins (and nucleic acids). As a consequence, these antibodies form immune complexes that activate complement and damage tissues, a type III hypersensitivity.

Which of the following statements is TRUE regarding Hemolytic Disease of the Fetus/Newborn (HDFN) caused by ABO antibodies? a. fetal hemolysis is typically severe b. it cannot occurs during first pregnancy c. it is most common with O mothers and A babies d. It occurs less commonly than Rh HDFN

c. it is most common with O mothers and A babies HDFN caused by ABO incompatibility between mother and child is, in fact, the most common form of HDFN (though it is so mild that some don't even call it "HDFN"). In virtually all situations, ABO HDFN is seen with a group O mother and a group A or B child. Group O individuals carry IgG ABO antibodies that, unlike the primarily IgM antibodies in non-group O people, are transported across the placenta and enter the fetal circulation. These antibodies (either anti-A, anti-B, or anti-A,B) are "naturally occurring," like all ABO antibodies, so the interaction may occur during the first pregnancy (unlike the classic form of HDFN due to Rh antibodies, which usually occurs in second pregnancies and beyond). However, the relatively weak ABO antigen expression on the surface of fetal and neonatal red cells means that the clinical and laboratory sequelae (including hemolysis) of ABO HDFN are usually not severe. In fact, affected babies may have a negative direct antiglobulin test (DAT).

Innate lymphoid cells? a. Are the most numerous leukocyte population b. Consist of B-cells c. Contain conspicuous cytoplasmic granules d. Are found in the peripheral blood and tissue

d. Are found in the peripheral blood and tissue Explanation: Innate lymphoid cells are NK cells which can be found in the peripheral blood and in many tissues. Neutrophils are the most numerous leukocyte population. NK cells do not contain conspicuous cytoplasmic granules. Innate lymphoid cells do not include B cells, which are part of the adaptive immune system.

Epitope-specific receptors of T lymphocytes are found? a. As either cytosolic or membrane-bound proteins b. In blood plasma, lymph, and other secretory fluids c. On the surface of plasma cells d. As transmembrane polypeptides e. In the nuclear lipid bilayer

d. As transmembrane polypeptides Explanation: The epitope-specific receptors of T-cells (TCRs) are displayed as membrane-bound molecules on their cell surfaces. TCRs are not found as soluble molecules. Epitope-specific molecules produced by plasma cells are genetically distinct from T-cell receptor molecules.

The Foxp3 nuclear transcription factor is expressed within? a. B-cells b. CD4+/CD8+ (double positive) thymocytes c. CD8+ cytotoxic cells d. CD4+CD25+ T regulatory cells e. Th2 cells

d. CD4+CD25+ T regulatory cells Explanation: Expression of the Foxp3 nuclear transcription factor is a distinctive feature of CD4+CD25+ Treg cells. Foxp3 is not expressed by any of the other cell types indicated.

A 2-month-old male infant presents with persistent diarrhea, signs and symptoms of Pneumocystis carinii pneumonia, and an oral fungal infection with Candida albicans. His weight is in the 10th percentile. Test results for HIV are negative by polymerase chain reaction. The most likely cause of these findings is? a. Grossly reduced levels of B-cells b. An X-linked inheritance of HLA genes c. Defective isotype switching d. Defective T-cell function e. Selective IgA deficiency

d. Defective T-cell function Explanation: The fungal infection is highly suggestive of a T-cell defect. Choices A, C, and E do not of themselves imply a deficiency in T-cell function. HLA genes are autosomal dominantly inherited, not X-linked.

A 2-month-old male infant presents with persistent diarrhea, signs and symptoms of Pneumocystis carinii pneumonia, and an oral fungal infection with Candida albicans. His weight is in the 10th percentile. Test results for HIV are negative by polymerase chain reaction. The most likely cause of these findings is? a. Markedly reduced levels of B-cells b. Lysosomal dysfunction c. Defective isotype switching d. Defective T-cell function e. Selective IgA deficiency

d. Defective T-cell function The fungal infection is highly suggestive of a T-cell defect. The other choices do not of themselves imply a deficiency in T-cell function.

A 12-year-old boy comes to the emergency department with a body temperature of 103.7°F. Which of the following substances is most likely responsible for his fever? a. IL-2 b. IFN-alpha c. IL-5 d. IL-6 e. IL-8

d. IL-6 Explanation: The pyrogens (pro-inflammatory cytokines) include IL-1, IL-6, and TNF-alpha. IL-2 plays a role in T-cell mediated immunity. IL-5 is for eosinophil growth. IL-8 is a neutrophil chemokine.

In positive selection, thymocytes that are eliminated are? a. Single positive CD4 cells b. Single positive CD8 cells c. Destined to become B-cells d. Incapable of recognizing self MHC e. Released from the thymus as T-cells

d. Incapable of recognizing self MHC Explanation: Double positive (DP) thymocytes incapable of recognizing self MHC are eliminated during positive selection. Single positive CD4 and CD8 cells have survived the positive selection process. DP cells whose CD8 molecules have engaged pMHC I, then cease to express CD4 molecules and become single positive (SP) CD8+ cells. Those bound to pMHC II stop expressing CD8 and become SP CD4+ cells. Thymocytes cannot switch to the B-cell developmental pathway. The only thymocytes released from the thymus as T-cells are those that have passed negative selection after positive selection

People with cystic fibrosis have recurrent infections with bacteria such as Pseudomonas aeruginosa because of respiratory tract changes that include a(n)? a. Decrease in lysozyme secretion b. Decrease in mucus secretion c. Decrease in pH allowing for microbial growth d. Increase in viscosity of secretions, resulting in difficulty expelling entrapped microbes e. Increase in watery secretions that are ineffective at entrapping organisms

d. Increase in viscosity of secretions, resulting in difficulty expelling entrapped microbes Explanation: The genetic defect in cystic fibrosis causes the mucus to be thick and viscous which makes it difficult to expel the entrapped microbes. Decreased pH is supposed to inhibit microbial growth.

A 6-month-old girl is brought to the pediatrician with a 2-week rash on the scalp. The patient has had fever, decreased appetite, and loose stools for the past week. The patient had two previous hospitalizations for the treatment of omphalitis. Physical examination shows a dehydrated baby whose scalp has an erythematous rash with focal necrosis and no pus. Laboratory studies show a WBC count of 37,000/mm³. Which of the following is the underlying mechanism of the child's most likely illness? a. Cytokine storm b. Defective microtubules c. Lack of generation of reactive oxygen species d. Lack of neutrophil adherence and extravasation e. Defective lysosomes

d. Lack of neutrophil adherence and extravasation Explanation: LAD presents with severe bacterial infections and neutrophilia; the first presenting sign is often delayed separation of the umbilical cord, resulting in omphalitis. LAD is caused by a decreased expression or function of integrin protein which interferes with the extravasation of neutrophils to sites of infection.

A 45-year-old man comes to the office and reports occasional spontaneous episodes of swelling in his arms, face, and genitals that resolve within 2 to 3 days. These episodes often are associated with abdominal pain and diarrhea. His father had similar symptoms. His blood pressure is 160/90 mm Hg. The physical examination is normal. Which of the following drugs should be avoided in the management of this patient's hypertension? a. Amlodipine b. Furosemide c. Hydrochlorothiazide d. Lisinopril e. Losartan f. Propranolol

d. Lisinopril Explanation: Hereditary angioedema is an inherited disorder of deficient or dysfunctional C1 esterase inhibitor, leading to ↑ levels of bradykinin and C1 complement pathway products, which increase vascular dilation and permeability associated with angioedema. ACE breaks down bradykinin, and therefore ACE inhibitors (drugs that end in "-pril") should be avoided in patients with HAE due to ↑ swelling and risk of airway compromise.

The primary lymphoid organs are those in which? a. Adaptive immune responses are usually initiated b. Filtration devices remove foreign matter c. Large numbers of circulating leukocytes make contact with one another d. Lymphocytes undergo their initial differentiation e. Pattern recognition receptors bind antigens

d. Lymphocytes undergo their initial differentiation Primary lymphoid organs are sites where lymphocytes undergo their initial differentiation. Adaptive immune responses are initiated by mature lymphocytes that have migrated out of primary lymphoid organs. Secondary lymphoid organs contain filtration devices to remove foreign materials. Circulating leukocytes are found within blood and lymph and secondary lymphoid organs but not within primary lymphoid organs. Pattern recognition receptors (PRRs) are expressed by cells of the innate immune system.

A 2-year-old boy is brought to the clinic because of a rash on his leg. He has a history of multiple skin infections with Staphylococcus aureus and a pulmonary infection with Aspergillus last year. Previous flow-cytometry studies revealed that the patient's blood neutrophils did not produce detectable levels of fluorescence. The activity of which of the following is most likely decreased in this patient? a. Phagolysosomal formation b. Neutrophil chemotaxis c. NK cell activity d. NADPH oxidase e. Perforin

d. NADPH oxidase Explanation: CGD is a phagocytic disorder associated with recurrent infections (eg, Aspergillus). It can be diagnosed using the Dihydrorhodamine test or dichlorofluoroscein test which shows failure to detect fluorescence by flow cytometry. CGD is caused by a defect in NADPH oxidase activity.

B lymphocytes synthesize and express immunoglobulin: a. Containing multiple epitope specificities b. In cytoplasmic phagosomes c. In membrane complexes also containing CD3 d. On their cell membrane surface

d. On their cell membrane surface Explanation: B cells synthesize and express immunoglobulin on their cell surfaces. Immunoglobulins within an individual B cell contain specificity for one epitope, not several. Cytoplasmic phagosomes are involved in degradation of unwanted materials. Membrane complexes also containing CD3 are T cell receptors (TCR) on the surfaces of T cells.

A 71-year-old female patient develops fever and inflammation of her left knee 3 days after discharge from the hospital following knee replacement surgery. Staphylococcus epidermidis organisms causing her infection are initially not targets of the patient's phagocytic cells. However, after IgG1 antibodies bind to their capsules, many S. epidermidis cells are readily destroyed via phagocytosis. This process of antibody-enhanced phagocytosis is known as? a. Affinity maturation b. Agglutination c. Neutralization d. Opsonization e. Precipitation

d. Opsonization Explanation: Antibodies bind to a single specific epitope on an antigen to identify them or tag them for destruction by other elements of the immune system in a process called opsonization. Neutralization is the blocking by antibody of structures on microbes and toxins that allow them to bind to host cell surfaces. Affinity maturation allows for enhanced binding of the antigen to the receptors. Agglutination causes RBC adherence and precipitation involves turning a soluble object into a solid precipitant.

The process that is synergistically enhanced by the binding of both antibodies and complement fragments such as C3b by phagocytes is known as? a. Agglutination b. Complement activation c. Neutralization d. Opsonization e. Precipitin reaction

d. Opsonization Explanation: Opsonization is the ↑ phagocytic uptake of cells or molecules as a result of opsonization when the microbe is tagged by antibodies (usually IgG) or membrane-bound C3b. Agglutination is the aggregation or clumping of cells or particles bound together by antibodies (usually IgM or dimeric IgA). Complement activation is initiated by the attachment of the C1 component of complement to epitope-bound antibody (IgM or IgG). Neutralization is the blocking by antibody of structures on microbes and toxins that allow them to bind to host cell surfaces. The precipitin reaction results from the assembly of large antigen-antibody complexes that precipitate from solution.

A 3-year-old boy with a history of recurrent bacterial and fungal infections is seen by his pediatrician for a new skin abscess in the left axilla. Many of his previous skin abscesses have been positive for Staphylococcus aureus. On physical examination, there is generalized lymphadenopathy, hepatomegaly, and flaky plaques on his arms and legs. A diagnosis is confirmed with a test in which nitroblue tetrazolium dye is used. Which of the following is a substrate for the enzyme that is most likely deficient in this patient? a. Carbon dioxide b. Hydrogen peroxide c. Lactic acid d. Oxygen e. Phosphoenolpyruvate f. Superoxide

d. Oxygen Explanation: CGD presents with recurrent infections due to a lack of NADPH oxidase, a key enzyme used by neutrophils to destroy pathogens via respiratory burst. NADPH oxidase uses oxygen as a substrate to produce superoxide anion, which is used to generate hydrogen peroxide and ultimately hypochlorous acid.

Pattern recognition receptors bind to? a. B and T lymphocytes b. MHC I molecules c. Natural killer cells d. Pathogen-associated molecular patterns

d. Pathogen-associated molecular patterns Explanation: Pattern recognition receptors (PRRs) bind to pathogen associated molecular patterns (PAMPs). PRRs cannot recognize host-associated molecules such as MHC class I molecules or host cells such as B, T, or NK cells.

The initial activation of the immune response to infections are due to interactions between? a. B cells and virus b. Natural killer cells and MHC I molecules c. T cells and virus peptides d. Pattern recognition receptors and virus RNA e. Antibody molecules and virus spike proteins

d. Pattern recognition receptors and virus RNA Explanation: Pattern recognition receptors bind to viral RNA and induce innate immunity activation to initiate the immune response against the pathogen. Innate immune system barriers are the first line of defense. Natural killer cells of the innate immune system are the second line of defense. T and B cells with antibodies of the adaptive immune system are the third level of defense.

A plasma cell has developed from a B cell. Compared to the cell from which it was derived, the plasma cell? a. Displays more peptides on MHC class II b. Is a more efficient antigen-presenting cell c. Recognizes different epitopes d. Releases soluble immunoglobulins e. Undergoes more efficient isotype switching

d. Releases soluble immunoglobulins Explanation: Plasma cells are different from B-cells in that they can secrete immunoglobulins/antibodies, but cannot do any of the other options listed. B-cells can recognize specific epitopes, display antigens on MHC class II proteins and are considered an antigen-presenting cells, and undergo isotype switching. Please note that both B-cells and plasma cells that are derived from a single clone can only recognize one specific epitope or antigen, but there are many other B-cell clones that can recognize other epitopes.

A receptor found on a monocyte binds to lipopolysaccharide on gram-negative bacteria. That receptor is most likely a member of which receptor family? a. Complement receptors b. Killer activation receptors c. Surface immunoglobulin receptor d. Toll-like receptors

d. Toll-like receptors Explanation: Toll-like receptors (TLRs) are a special type of extracellular/membranous pattern recognition receptors (PRRs) that are present on phagocytes. Complement receptors bind C3b and facilitate the phagocytosis of foreign cells. Natural killer cells use killer activation receptors that detect stress molecules expressed on unhealthy host cells that infected or tumor cells. Surface immunoglobulin receptors are only found on B cells.

A 22-year-old man comes to the office with diarrhea for 3 weeks. He recently received an allogeneic donor bone marrow transplant for treatment of his leukemia. His physical exam is shown below. Laboratory studies show: Aspartate aminotransferase of 432 U/L Alanine aminotransferase of 356 U/L Alkaline phosphatase of 400 U/L Bilirubin of 3 mg/dL Which of the following events most likely led to this patient's current condition? a. Medication side effect b. Immediate postoperative complication c. Reaction to blood type incompatibility d. Transplantation

d. Transplantation Acute GVHD presents with a triad of dermatitis, hepatitis, and gastroenteritis and occurs after transplantation. While medications can also cause a rash, the triad of rash, diarrhea, and hepatitis after transplantation is more consistent with GVHD.

Which of the following is initiated by the interaction of host cell membranes with IgM or IgG antibody without immune complex formation? a. Arthus reaction b. Serum sickness c. Type I hypersensitivity reaction d. Type II hypersensitivity reaction e. Type IV hypersensitivity reaction

d. Type II hypersensitivity reaction Type II hypersensitivity reactions occur with host cell membranes or with the extracellular matrix. Arthus reactions and serum sickness are type III hypersensitivities that result from the interaction(s) of antibody with soluble antigen(s) that produces an immune complex. IgE is not listed here, thus ruling out type I hypersensitivity.

An 18-year-old male prevents with fever, headache, and nuchal rigidity. Gram stain of his cerebrospinal fluid is shown below. This is his third episode of meningitis in the last 5 years. Which of the following is most likely deficient in this patient? (Gram stain of patient's cerebrospinal fluid.) a. C1 b. C3b c. C5a d. C4 e. C5-9

e. C5-9 Explanation: Deficiency of C5-9 which makes up the membrane attack complex or MAC leads to ↑ susceptibility to Neisseria infections.

A 48-year-old man with a transplanted kidney comes to the hospital because of body aches, low-grade fever, and reduced urine volume for the past 4 days. He underwent uncomplicated cadaveric kidney transplant 3 weeks ago. Urinalysis shows no bacteria or crystals. His serum creatinine is 2.8 mg/dL, increased from 1.7 mg/dL in the immediate postoperative period. Which of the following markers is most likely to be found on the surface of the cells that are causing the damage to tubular cells? a. CD19 b. CD20 c. CD22 d. CD56 e. CD8

e. CD8 Acute rejection is seen most often in the first 3 months after transplantation due to human leukocyte antigen discrepancies. Acute transplant rejection is predominantly mediated by cytotoxic T-cells (CD8), leading to cytotoxic graft cell death and release of proinflammatory cytokines.

Positive selection refers to? a. B-cell activation by an antigen b. T-cell independent activation with C3b c. Removal of a B-cell from circulation due to high self-antigen binding d. Production of memory B-cells e. Detection of a functional B-cell receptor

e. Detection of a functional B-cell receptor Explanation: In positive selection, Bruton's tyrosine kinase (BTK) must detect a functional IgM BCR in order for the B-cell to survive, divide, mature, and differentiate. Removal of a B-cell from circulation due to high self-antigen binding refers to negative selection, which occurs after positive selection. B-cell activation by an antigen, T-cell independent activation with C3b, and production of memory B-cells occur after positive and negative selection.

Which of the following antibody isotypes stimulates the classic pathway of the complement system? a. IgA and IgD b. IgA and IgE c. IgA and IgM d. IgE and IgG e. IgG and IgM

e. IgG and IgM Explanation: The classical pathway of complement is initiated by the interaction of C1 with IgG or IgM. IgA, IgD, and IgE do not bind to C1.

Which is the best isotype for agglutination? a. IgA antibodies b. IgD antibodies c. IgE antibodies d. IgG antibodies e. IgM antibodies

e. IgM antibodies IgM is the largest immunoglobulin and has 10 epitope-binding sites (valence). Its relatively large span and valence make it very efficient at cross-linking epitopes on adjacent particles. Other isotypes, because of their smaller size and lesser valence, are less efficient in direct agglutination.

A previously healthy 17-year-old male patient presents for evaluation of recent-onset severe pain in his knees and elbows. He is febrile and examination reveals a rash on his trunk, arms, and legs. His past medical history is unremarkable, and he is up-to-date on all immunizations. Further questioning reveals that he had a sore throat about 3 weeks ago that was positive for streptococcal rapid antigen test. The signs and symptoms experienced now by this patient are most likely the result of a/an? a. Allergic reaction b. Cell-mediated hypersensitivity c. Cytotoxic reaction d. Contact dermatitis e. Immune complex disease

e. Immune complex disease Post-streptococcal glomerulonephritis is caused by a immune complex deposition, which is a type III hypersensitivity.

A naive B-cell is migrating from the blood into a lymph node and first rolls along high endothelial venules of the lymph node. Which of the following is expressed by the B-cell to facilitate the rolling process? a. C3a b. CD20 c. IgA d. IgM e. Integrin

e. Integrin Sialyl Lewis, integrins, and selectins are expressed on leukocytes for adhesion to the endothelial cells. The endothelial cells also express selectins.

Which of the following molecules is expressed on activated T-cells to limit their expansion and activity? a. CD4 b. CD28 c. CD40 d. IL-2R e. PD-1

e. PD-1 Explanation: Engagement of PD-1 on activated T-cells by PD-L1/L2 limits TCR and costimulatory molecule signaling to dampen T-cell-mediated responses. Antibodies to this interaction are currently being used to increase antitumor immune responses that tend to be turned off by the tumor. CD4 and CD28 are expressed on resting and activated T-cells and promote the expansion and activation of T-cells. CD40 is expressed on B-cells, and IL-2R promotes the expansion and activation of T-cells.

A 56-year-old woman develops fever and decreased urine output 1 hour after receiving an unrelated-donor kidney transplant. Her blood type is B, Rh-positive. Records were reviewed and the donor was seen to have blood type A, Rh-negative. Which of the following best describes the mechanism of transplant rejection that is occurring in this patient? a. Donor T-cells b. Donor macrophages c. Donor preformed anti-recipient antibodies d. Recipient T-cells e. Recipient preformed anti-donor antibodies

e. Recipient preformed anti-donor antibodies Hyperacute rejection occurs within minutes to hours of transplantation and leads to hemorrhage and necrosis of the transplanted kidney. Hyperacute rejection is mediated by preformed antibodies from the recipient.

DiGeorge syndrome is an immune deficiency disease resulting from impaired thymic development. Which of the following is/are affected in patients with DiGeorge syndrome? a. B-cell development only b. Complement only c. NK cell function d. T-cell development only e. T-cell and B-cell functions

e. T-cell and B-cell functions The defective thymic environment inhibits T-cell development and function. Because so much B-cell activity depends on interaction with T-cells, B-cell responses will also be impaired. Complement would not be impaired while sparing T and B-cell activity. NK cell function should not be affected.

The thymus is the site of initial differentiation for? a. B-cells b. Erythrocytes c. Hematopoietic stem cells d. NK cells e. T-cells

e. T-cells The thymus is the site of initial differentiation of T cells. Erythrocytes develop from erythroid precursors in the bone marrow. Hematopoietic stem cells differentiate along any one of several lineages within the bone marrow. Natural killer (NK) cells develop within the bone marrow and lack rearranged TCR.

Which of the following is true regarding antibodies? a. Are synthesized and secreted by both B and T cells b. Bind to several different epitopes simultaneously c. Contain four different light chain polypeptides d. Recognize specific epitopes with self molecules e. Tag antigens for destruction and removal

e. Tag antigens for destruction and removal Explanation: Antibodies bind to a single specific epitope on an antigen to identify them or tag them for destruction by other elements of the immune system in a process called opsonization. They are synthesized only by B cells and plasma cells. An antibody contains two identical light chains and two identical heavy chains. Immunoglobulins within an individual B cell contain specificity for one epitope, not several. Self-recognition is not required for antibody molecules.

Which of the following CD4+ T-cell subsets secretes chemokines and cytokines that recruit neutrophils important for mediating antifungal responses? a. Treg b. Tfh c. Th1 d. Th2 e. Th17

e. Th17 Explanation: Th17 secrete IL-17 and chemokines that recruit neutrophils and are important for fighting certain fungal pathogens. Th1 cells can direct immune responses against intracellular pathogens, and Th2 cells are important for extracellular pathogen responses, such as helminths. Tregs are important for controlling immune responses targeted against self.

A 19-year-old female presents for evaluation of a burning sensation while urinating and a thick white vaginal discharge. She recently completed a 10-day course of antibiotics to treat strep throat. She is diagnosed with a Candida albicans infection and advised to purchase an over-the-counter antifungal cream. However, she decides against using the antifungal medication and her signs and symptoms resolve spontaneously within a week. Her infection was most likely cleared mainly by the action of? a. B-cells b. CD8+ T-cells c. Cytokines d. Th1-directed cell-mediated responses e. Th17 cells

e. Th17 cells Explanation: Candida albicans is an extracellular fungus, and the innate immune system will be the initial sources of protection. Extracellular fungi trigger various adaptive immune responses, including the generation of Th17 cells that are the primary means for clearing fungal infections. Antifungal antibodies produced during the course of the adaptive responses against fungi are sometimes ineffective in clearing fungal infections and can become the basis for hypersensitivity responses triggered by fungal infections. Th1-directed cell-mediated responses are important for the control of intracellular fungi.

Negative selection of T-cells occurs in the? a. Blood vessels b. Bone marrow c. Lymph node d. Thymus cortex e. Thymus medulla

e. Thymus medulla Explanation: Negative selection of T-cells occurs as they move from the thymic cortex into the thymic medulla. It does not occur at sites outside of the thymus.

An 8-year-old patient received a bracelet as a gift. Two days later, she developed itchiness in her hands, and her mother noticed that they were bright red. Her mother also noticed clear fluid vesicles on her right forearm. These findings suggest which type of hypersensitivity? a. Type I, mediated by CD4+ T-cells b. Type I, mediated by CD8+ T-cells c. Type II, mediated by CD8+ T-cells d. Type III, mediated by CD4+ T-cells e. Type IV, mediated by CD4+ T-cells

e. Type IV, mediated by CD4+ T-cells The urticaria (itchiness) and fluid vesicles on her forearm are hallmarks of contact dermatitis, a type IV hypersensitivity mediated by CD4+ T-cells. Type I and type II, and type III hypersensitivities are mediated by antibodies; type IV is not.

The term applied to the interaction of soluble antigen with soluble antibody that results in the formation of insoluble antigen-antibody complexes is? a. agglutination b. complement activation c. neutralization d. opsonization e. precipitin reaction

e. precipitin reaction The precipitin reaction results from the assembly of large antigen-antibody complexes that precipitate from solution. Agglutination is the aggregation or clumping of cells or particles bound together by antibodies. Complement activation is initiated by the attachment of the C1 component of complement to epitope-bound antibody (IgM or IgG). Neutralization is the blocking by antibody of structures on microbes and toxins that allow them to bind to host cell surfaces. Opsonization is the increased phagocytic uptake of cells or molecules tagged by antibodies (usually IgG or IgM).

A 15-year-old boy comes to the emergency department with an erythematous, tender lesion on his right knee. He scraped his knee after falling off a bicycle 2 days ago. The physical examination shows a 3 cm × 2 cm area of induration, and a thick white fluid can be expressed from the lesion. A smear of the fluid is shown. Which of the following substances is most likely responsible for recruiting the predominant cell type shown in the smear to the site of injury? a. Interleukin-1 b. Interferon-gamma c. TNF-alpha d. Interleukin-5 e. Interleukin-6 f. Interleukin-8

f. Interleukin-8 Explanation: Neutrophils are the primary leukocytes in pus and can be identified by their size (twice that of an RBC) and multilobed segmented nuclei. IL-8 attracts neutrophils to the site of inflammation and is secreted by mostly macrophages. IL-1 and IL-6 are pyrogens and initiate inflammation and fever. IL-5 and IL-8 is for eosinophil growth, differentiation, and chemotaxis. Interferon-gamma activates macrophages.