Immunology Book Questions (CH 1-4 & 6)
4-4: A protein epitope formed as a result of three-dimensional folding of the protein, and which is destroyed if the protein denatures, is called a _______ epitope. A. linear B. multivalent C. conformational D. complementarity E. framework.
C
3-13: Systemic distribution of TNF-α in the blood circulation may cause _____. a. respiratory burst b. the interferon response c. activation of the lectin pathway of complement d. hypertension e. septic shock.
E
6-14: Yasuo Yamagata, a 63-year-old, experienced severe back pain for several weeks before visiting his family physician. He also complained of fatigue and looked pale. Blood analysis revealed a red blood cell count of 3.2 × 106/ȝl (normal 4.2-5.0 × 106/ȝl), a white blood cell count of 2800/ȝl (normal 5000/ȝl), a sedimentation rate of 30 mm/h (normal <20 mm/h) and a serum IgG of 4500 mg/dl (normal 600-1500 mg/dl). IgA and IgM levels were well below normal. Skeletal survey showed lytic lesions in vertebrae, ribs and skull. A bone marrow sample revealed 75% infiltration with plasma cells. Elevated protein in urine was confirmed to be Bence-Jones protein (immunoglobulin light chains). The patient was diagnosed with IgG Ȝ multiple myeloma and began an immediate chemotherapy regime. Which of the following would be consistent with this type of malignant tumor of plasma cells? A. Serum IgG is polyclonal. B. Anemia and neutropenia are present as the result of plasma-cell infiltration in the bone marrow and consequent limitation of space. C. Susceptibility to pyogenic infections is unaffected. D. Serum IgG consists of IgG1, IgG2, IgG3, and IgG4 in approximately equal proportions. E. ț and Ȝ light chains are found in excessive quantities in the urine.
The correct answer is b. Multiple myeloma results from the outgrowth of a single plasma cell that has undergone malignant transformation in the bone marrow. Tumor masses expand to the point at which the relatively limited amount of space available in the bone becomes filled with tumor cells, constraining the development of erythrocytes and neutrophils and causing anemia and neutropenia, respectively. Serum IgG would be predominantly monoclonal, because the tumor derives from a single plasma cell. Similarly, the Bence-Jones protein would be of the Ȝ type, not ț, because this is an IgG Ȝ multiple myeloma. Patients with multiple myeloma would be susceptible to pyogenic infections because the diversity of their immunoglobulins is limited, making these patients immunocompromised.
6-15: Thomas Harrison, born at 39 weeks after an uneventful pregnancy, developed normally and thrived for the first 8 months of infancy. During the next 12 months he received antibiotics for a number of infections including two episodes of acute otitis media (middle ear infection), sinusitis, and superficial cellulitis (streptococcal skin infection) on his left thigh. Two days ago, after an upper respiratory infection, Thomas developed a fever, became drowsy, and experienced a seizure. Lumbar puncture confirmed Haemophilus influenzae type B (HiB) in the cerebrospinal fluid. Intravenous ceftriaxone was administered and his condition stabilized after 24 hours. Laboratory results showed his total lymphocyte count to be normal; however, flow cytometry using antibodies for the B-cell marker CD19 revealed an absence of B cells. Antibodies against CD3, CD8, and CD4 revealed the presence of cytotoxic and helper T cells. Serum IgG and IgM levels were remarkably low at 75 mg/dl and 10 mg/dl, respectively (IgG normally 600-1500 mg/dl; IgM 75-150 mg/dl), and IgA was undetectable. Family history showed that neither of Tomas's two older sisters (ages 4 and 7) had experienced recurrent infections like this in infancy. Thomas's maternal aunt had a boy of about the same age as Thomas who had also been experiencing repeated episodes of otitis media, sinusitis, and, most recently, a severe case of pneumonia, all caused by pyogenic bacteria and treated successfully with antibiotics. Thomas began intravenous IgG replacement therapy administered at 3-4-week intervals, and his repeated episodes of infection abated. These findings are most consistent with a diagnosis of A. hyper-IgM syndrome B. X-linked agammaglobulinemia (XLA) C. chronic granulomatous disease (CGD) D. DiGeorge syndrome E. MHC class I deficiency.
The correct answer is b. XLA is an X-linked recessive condition affecting males and is characterized by the absence of B cells and serum immunoglobulins owing to a defect in B-cell development. Specifically, Bruton's tyrosine kinase (Btk) is defective, which compromises normal signaling properties needed for progression through the stages of B-cell development. Te absence of serum IgG and IgM makes these patients particularly susceptible to infections with bacteria that are encapsulated, because such patients are unable to phagocytose these pyogenic bacteria by means of Fc receptors, having to rely only on complement activation and opsonization for clearance. The absence of IgM rules out hyper-IgM syndrome. CGD, although an X-linked disease, is not associated with hypogammaglobulinemia; persistent antigenic stimulation in CGD causes hypergammaglobulinemia. The presence of CD4 and CD8 T cells rules out both DiGeorge syndrome and bare lymphocyte syndrome type I (MHC class I deficiency), in which either a complete absence of T cells or an absence of CD8 T cells is expected, respectively.
1-4: Which of the following is not a characteristic of inflammation? A. inactivation of macrophages B. increased vascular permeability and edema C. vasodilation D. pain E. influx of leukocytes.
A
1-5: The processes of clonal selection and clonal expansion occur during _____. A. adaptive immune responses B. innate immune responses C. hematopoiesis D. self renewal E. immunodeficiency diseases.
A
1-6: The _____ is (are) the lymphoid organ(s) that filter(s) the blood. A. spleen B. tonsils C. Peyer's patches D. appendix E. adenoids.
A
1-9: Which of the following pairs is mismatched? A. plasma cell: mediation of phagocytosis and killing of microorganisms in the plasma B. megakaryocyte: formation of platelets C. dendritic cell: activation of adaptive immune responses D. natural killer cell: develops from a common lymphoid progenitor E. neutrophil: formation of pus F. regulatory T cell: inhibition of T-cell activity.
A
2-13: At which anatomical location do Paneth cells reside? A. crypts of the intestinal tract B. the lining of blood vessels C. in the urogenital tract D. in the liver adjacent to Kupfer cells E. alveolar spaces of the respiratory tract.
A
3-4: Which of the following pairs is mismatched? A. catalase: hydrogen peroxide production B. bactericidal permeability-increasing protein: binds LPS and kills Gram-negative bacteria C. elastase: basement membrane degradation D. NADPH oxidase: superoxide radical production E. gelatinase: iron sequestration F. paracrine: acts on neighboring cells.
A
4-2: When IgG is cleaved with a protease that targets the hinge region, which of the following is generated? A. two Fab fragments and one Fc fragment B. two Fc fragments and two Fab fragments C. Fc fragments that bind antigen D. Fab fragments that facilitate antibody effector function E. a membrane-bound form of antibody.
A
6-10: _______ involves successive rearrangement at the light- chain loci when reactivity to self antigen occurs during B-cell development. A. receptor editing B. somatic hypermutation C. chromosomal translocation D. clonal deletion E. anergy.
A
6-12: Immature B cells specific for monovalent self antigens encountered in the bone marrow A. enter a state of developmental arrest known as anergy B. express abnormally high levels of IgM on the cell surface C. can become activated but only if IgD is no longer expressed on the cell surface D. never leave the bone marrow and die by apoptosis E. engage in the process of receptor editing.
A
6-4: Which of the following events is not associated with the establishment of allelic exclusion of immunoglobulin heavy-chain loci? A. active transcription of RAG1 and RAG2 B. degradation of RAG proteins C. expression of only one productively rearranged heavy-chain locus D. remodeling of chromatin structure of heavy-chain locus so that it resists gene rearrangement E. formation of a functional pre-B-cell receptor.
A
6-6: Developing B cells that fail to make productive D to J heavy-chain rearrangements on both homologous chromosomes A. die by apoptosis in the bone marrow B. will rearrange heavy-chain loci multiple times until a productive rearrangement is made C. undergo clonal proliferation D. upregulate expression of transcription factors E2A and EBF E. fail to rearrange V to DJ.
A
6-13A: B-cell tumors originate during different developmental stages of B cells during their maturation in the bone marrow or after maturation and export to the periphery. A. Explain why B cells isolated from a particular B-cell tumor all express the same immunoglobulin.
A B-cell tumor comprises cells derived from a single cell that has undergone transformation, resulting in uncontrolled growth. No further maturation of the B cell occurs after transformation. If the B cell has rearranged the heavy-chain and light-chain genes before transformation, then immunoglobulin will be expressed at the cell surface. Because all of the cells in the tumor belong to the same clone, the immunoglobulin on all of them will be made of the same heavy and light chains.
3-7: Using the table below: A). match the local and systemic effects in column A with the appropriate cytokine in column B. Note that more than one answer in column B may be used. B). (i) Which of these cytokines are produced by macrophages? (ii) Which cells produce the other(s)? Column A A. activation of blood-vessel endothelium B. fever C. induction of IL-6 synthesis D. increase in vascular permeability E. localized tissue destruction F. production of acute-phase proteins by hepatocytes G. induction of resistance to viral replication H. activation of NK cells I. leukocyte chemotaxis J. activation of binding by β2 integrins (LFA-1, CR3) K. septic shock L. mobilization of metabolites Column B 1. IL-1 2. IL-6 3. CXCL8 4. IL-12 5. TNF-α 6. type I interferons
A). A-1, 5; B-1, 2, 5; C-1; D-5; E-1; F-2; G-6; H-4, 6; I-3; J-3; K-5; L-5 B). (i) The cytokines IL-1, IL-6, CXCL8, IL-12, and TNF-α are produced by macrophages. (ii) Type I interferons can be produced by many different types of cell when infected with a virus. Specialized cells called plasmacytoid dendritic cells produce large amounts of type I interferons.
4-11: Match the antibody in Column A with its description or function in Column B. There may be more than one answer for each antibody. Column A A. IgA B. IgD C. IgE D. IgG E. IgM Column B 1. opsonin 2. complement activation 3. transport across placenta 4. most abundant in serum 5. most abundant in mucosal secretions (for example, colostrum) 6. sensitization of mast cells 7. sensitization of basophils 8. sensitization for killing by NK cells 9. more made in body than any other antibody 10. least abundant in serum
A-1, 2, 5, 9; B-7; C-6, 7, 10; D-1, 2, 3, 4, 6, 8; E-2
2-9: Match the term in column A with its description in column B. Column A A. classical pathway of complement activation B. C3b2Bb C. C3 D. properdin E. anaphylatoxins Column B 1. activated by C-reactive protein or antibody 2. produces C5a and C5b 3. contains a thioester bond that is susceptible to nucleophilic attack 4. protects C3bBb from protease degradation 5. induce local and systemic inflammatory responses
A-1; B-2; C-3; D-4; E-5
1-3: Match the term in column A with its description in column B. Column A A. defensins B. lymph C. mucosae D. edema E. complement Column B 1. bathed in antimicrobial fluids that protect underlying epithelial surfaces 2. membrane-disrupting cytotoxic peptides 3. accumulation of fluid across permeable endothelium 4. a combination of cells and fluid that is transported to the lymphatics 5. proteins in the serum that tag pathogens for destruction by effector cells
A-2; B-4; C-1; D-3; E-5
3-3: Match the receptor in column A with its ligand in column B. Column A A. NOD2 B. TLR4 C. dectin-1 D. CR3/CR4 E. NOD1 F. SR-A G. TLR9 Column B 1. carbohydrate 2. muramyl dipeptide 3. γ-glutamyl diaminopimelic acid 4. teichoic acid 5. lipopolysaccharide (LPS) 6. flamentous hemagglutinin 7. unmethylated CpG-rich nucleotide motif
A-2; B-5; C-1; D-1, 5, 6; E-3; F-4, 5; G-7
2-12: Match the term in column A with its description in column B. Column A A. α2-macroglobulin B. defensins C. coagulation system D. bradykinin E. cryptdins Column B 1. amphipathic peptides making up two classes (α and β) that penetrate and disrupt microbial membranes 2. vasoactive peptide facilitating the recruitment of innate immunity mediators 3. a soluble protease inhibitor found in human plasma 4. inhibits dissemination of pathogens by forming blood clots 5. α-defensins made by Paneth cells
A-3; B-1; C-4; D-2; E-5
6-1: Match the stage of B-cell development in Column A with the rearrangement or expression status of the immunoglobulin genes in Column B. Column A A. immature B cell B. small pre-B cell C. large pre-B cell D. stem cell E. early pro-B cell F. late pro-B cell Column B 1. V-J rearranging 2. germline configuration of heavy and light-chain genes 3. V-DJ rearranging 4. ȝ heavy chain plus Ȝ or ț light chains on cell surface 5. VDJ rearranged but light-chain gene in germline configuration 6. D-J rearranging
A-4; B-1; C-5; D-2; E-6; F-3
6-11: Match the term/description in Column A with the process it induces/deploys in Column B. Column A A. non-lymphoid stromal cells of the bone marrow locus in a B cell B. allelic exclusion C. multivalent self antigens in the bone marrow D. non-lymphoid stromal cells of lymph node cortex E. monovalent self antigens in the bone marrow Column B 1. expression of only one heavy-chain locus and one light-chain 2. alteration of light-chain gene 3. chemokine-mediated recruitment of blood-borne B cells to high endothelial venules 4. establishment of an anergic state 5. provision of adhesion molecules and growth factors for B-cell development
A-5; B-1; C-2; D-3; E-4
4-3: Match the antibody term in Column A with its correct characteristics in Column B. Use each answer only once. Column A A. light chain B. hypervariable region C. constant region D. heavy chain E. framework region F. V domain Column B 1. the part of the antibody that binds antigen 2. contributes around 50 kDa to the overall molecular weight of IgG 3. comprises the β strands and loops not involved in antigen binding 4. the most conserved region of the molecule with limited variation between antibodies 5. located within a V domain and varies greatly between different antibodies 6. pairs with the amino-terminal part of a heavy chain to form one of the two arms of an antibody
A-6; B-5; C-4; D-2; E-3; F-1
4-10: A. Which of the IgG subclasses is most efficient at activating complement? B. Explain why. C. Which is least efficient and why?
A. IgG3 is most efficient at complement activation. B. The hinge region of IgG3 is the longest of all the IgG subclasses. Its length and flexibility make the IgG3 Fc region more accessible for binding C1 compared with the other IgG subclasses. C. IgG4 fails to activate complement because its Fc region binds C1 poorly.
1-10: The specialized cells that provide the interface between the lumen of the gut and the underlying lymphoid tissue _____. A. make up the germinal center B. are called the M cells C. are located in the periarteriolar lymphoid sheath D. are specialized in killing encapsulated bacteria E. are progenitors of monocytes.
B
2-1: Which of the following statements is incorrect? A. Mucosal surfaces are better than skin surfaces at supporting colonization by commensal microorganisms. B. The skin provides a larger surface area than mucosal surfaces for commensal microorganisms. C. There are ten times as many bacteria residing in the intestinal tract than the number of cells in the human body. D. It is common for commensal bacteria to live in symbiosis with their human hosts. E. During gestation in mammals, a fetus does not have any commensal microorganisms on their skin or mucosal surfaces.
B
2-5: All of the following are true of some or all complement proteins except _____. A. they are soluble and bind to pathogen surfaces B. they participate only in innate immunity C. they are present in extracellular fluids, blood, and lymph D. they facilitate the phagocytosis of pathogens E. they are made as zymogens.
B
3-2: Infammatory cytokines _____. A. are stimulated through scavenger receptors and not Toll-like receptors B. facilitate the migration of neutrophils from blood to infected tissues C. are produced only by phagocytic cells D. mediate direct dissociation of IțB from NFțB E. act as opsonins.
B
4-12: Humanized monoclonal antibodies are best described as ______? A. antibodies made in mice in which the mouse antibody genes have been replaced with human equivalents B. human antibodies in which the CDR loops have been replaced by mouse-derived CDRs of the desired specificity C. antibodies made in culture by human hybridomas D. antibodies containing mouse Fab regions of both the heavy and light chain and human Fc regions E. antibodies containing human Fab regions of both the heavy and light chain and mouse Fc regions.
B
4-9: The phenomenon of allelic exclusion ensures that B cells A. use only one V, D, and J segment during somatic recombination B. express only one type of heavy chain and one type of light chain C. do not undergo alternative splicing until cell proliferation commences D. do not secrete antibody until antigen is encountered E. carry out affinity maturation directed at heavy chains and not light chains F. derived from B-cell lymphomas are heterogeneous.
B
6-2: All of the following occur after B cells leave the bone marrow except A. peripheral tolerance B. receptor editing C. differentiation into plasma cells D. formation of follicular center cell lymphomas E. production of memory B cells F. recirculation between lymph, blood, and secondary lymphoid tissues.
B
3-1: Which of the following participates in an immediate rather than an induced innate immune response to infection in a human host? (Select all that apply.) A. scavenger receptors B. commensal microorganisms C. dectin-1 D. alternative pathway of complement activation E. MyD88 F. CXCL8 G. defensins H. NOD1 and NOD2 I. lectin pathway of complement activation.
B,D,G
3-10: Which of the following statements regarding TLR4 is false? (Select all that apply.) A. TLR4 is a Toll-like receptor expressed by macrophages, but not by NK cells. B. TLR4 is an example of a phagocytic receptor. C. TLR4 associates with CD14, which acts as a co-receptor to TLR4. D. The ligand for TLR4 is lipopolysaccharide (LPS). E. TLR4 is expressed as a homodimer on the cell surface. F. The extracellular domain of TLR4 associates with soluble MD2. G. TLR4 does not contain a cytoplasmic TIR domain.
B,G
2-11: Which of the following is not an example of a complement control protein? A. decay-accelerating factor (DAF) B. factor H C. factor B D. membrane cofactor protein (MCP) E. factor P (properdin) F. factor I.
C
2-2: All of the following are associated with the skin except _____. A. blood vessels B. a low surface density of putative pathogens C. specialized lymphoid tissues D. lymphatics E. an impenetrable physical barrier to microorganisms.
C
2-7: Which of the following does not describe the outcome of complement activation? A. chemotaxis B. opsonization C. vasoconstriction D. proteolysis E. membrane permeabilization.
C
3-5: The positive-feedback loop established between macrophages and dendritic cells in infected tissues involves the secretion of _____ by the macrophage and _____ by the NK cell. A. type I interferons; activating receptors B. IL-15; IL-12 C. IL-12; IFN-γ D. IFN-γ; cytotoxic granules E. ICAM-1; LFA-1.
C
4-1: The antigen-binding site of an immunoglobulin is formed from A. the V regions of light chains only B. the C regions of heavy chains only C. paired V regions of a single heavy chain and a single light chain D. paired V regions of two light chains E. paired C regions of two heavy chains.
C
4-6: Which of the following statements regarding the process of differential splicing of primary RNA transcripts encoding immunoglobulins is incorrect? A. It does not require rearrangement of genomic DNA sequences. B. It underlies the production of both membrane-bound IgM and IgD in naive B cells. C. It is the mechanism involved in isotype switching. D. It occurs during B-cell differentiation into plasma cells when antibodies are produced in their secreted form. E. It permits the production of different types
C
6-3: Stromal cells produce _______, which is a secreted B-cell development growth factor influencing progression of B cells from the late pro-B-cell to the pre-B-cell stage. A. stem-cell factor B. Kit C. IL-7 D. VLA-4 E. VCAM-1.
C
6-7: All of the following statements regarding immunoglobulin gene rearrangement are true except A. Non-B cells retain their chromatin containing the immunoglobulin loci in a 'closed' configuration. B. T-cells never transcribe immunoglobulin genes. C. There is only one promoter on the heavy-chain locus that is 5' of the V segments. D. Pax-5, a transcription factor, interacts with enhancer sequences positioned 3' of the heavy-chain C-region genes. E. Transcription of immunoglobulin loci precedes gene rearrangement.
C
4-7: Which of the following recombinations is not permitted during somatic recombination in the heavy-chain and light-chain immunoglobulin loci? (Select all correct answers.) A. DH:JH B. VȜ:JȜ C. Dț:VH D. VH:JH E. VH:DH.
C,D
3-11: Describe the properties of cytokines that help to protect the host from tissue damage during immune responses to infection.
Cytokines are relatively short-lived, which means that they must mediate their effects soon after their release as soluble proteins if they are to be functional. This property usually limits the actions of cytokines to within the immediate vicinity of their production. Sometimes the effects of cytokines are localized even more by direct contact between the cytokine-secreting cell and the responding cell bearing the specific cytokine receptor. These properties minimize systemic effects and confine immune responses to restricted locations, which affects a limited number of responding cells.
1-2: One reason that pathogenic microorganisms have an advantage in the host they infect is because they _______. A. have previously been encountered through natural exposure B. have previously been encountered through vaccination C. strengthen the host's immune response D. reproduce and evolve more rapidly than the host can eliminate them E. reproduce and evolve more slowly than the host can eliminate them.
D
1-8: Which of the following pairs is mismatched? A. T-cell activation: cell division and differentiation B. effector B cell: plasma cell C. plasma cell: antibody secretion D. helper T cell: kills pathogen-infected cells E. helper T cell: facilitates the differentiation of B cells.
D
2-3: Which of these pairs are mismatched? A. cytosol: intracellular pathogen B. surface of epithelium: extracellular pathogen C. nucleus: intracellular pathogen D. lymph: intracellular pathogen
D
2-6: A(n) _____ is an inactive form of an enzyme that frequently participates in a cascade of enzymatic reactions during complement activation. A. regulator of complement activation B. convertase C. complement control protein module D. zymogen E. opsonin.
D
2-8: All of the following are involved in the alternative pathway of complement activation except _____. A. factor B B. factor D C. factor P (properdin) D. C4 E. C5.
D
3-8: The early events of inflammation are characterized by all of the following except _____. a. vasodilation b. extravasation c. pain d. apoptosis e. increased vascular permeability f. chemotaxis.
D
4-14: Which of the following statements best explains why the immune system can continue to make antibodies after treatment with the anti-CD20 antibody rituximab? A. New CD20-positive B cells are reconstituted so quickly that antibody concentration during and after treatment is unafected. B. Rituximab stimulates B-cell proliferation, so for a short while after its administration there is actually an increase in antibody concentration. C. Rituximab is a mouse monoclonal antibody and therefore its Fc region is unable to bind to the surface receptors on human NK cells that bind to Fc. D. Plasma cells do not express CD20 on their cell surface, and antibody production by these cells continues unhampered. E. Rituximab stimulates anti-antibody production, leading to its rapid clearance by the body.
D
6-5: Multiple successive gene rearrangements at the immunoglobulin heavy-chain locus A. increase the likelihood that a functional heavy chain is formed B. always follow successive gene rearrangement of the immunoglobulin light-chain locus C. occur after the completion of the second checkpoint in small pre-B cells D. are not possible because the D segments are removed following the joining between D to J and V to DJ E. may result in the production of B cells expressing two different types of heavy chain.
D
4-5: The events listed below participate in the generation of junctional diversity. Put them in chronological order. A. DNA strands pair, and unpaired nucleotides are removed by exonuclease activity. B. P-nucleotides are generated after nicking of one DNA strand. C. DNA polymerase fills in gaps, and DNA ligation forms a coding joint. D. The RAG complex cleaves heptamer RSSs, and DNA hairpins are formed. E. Terminal deoxynucleotidyl transferase adds N-nucleotides to the 3' end of the stretch of P-nucleotides.
D>B>E>A>C
1-7: Which of the following best describes the movement of a T cell through a lymph node? A. It enters via efferent lymphatics and exits via the bloodstream. B. It enters via afferent lymphatics and exits via the bloodstream. C. It enters via the bloodstream and exits via afferent lymphatics. D. It enters via the bloodstream and exits via the bloodstream. E. It enters via the bloodstream and exits via efferent lymphatics.
E
2-10: The primary role of complement control proteins that operate in the early stages of complement activation is to _____. A. regulate the expression of complement proteins B. ensure that the components of the membrane-attack complex assemble in the correct sequence C. facilitate the secretion of complement proteins to extracellular locations D. stabilize complement proteins, thus extending their half-lives in serum E. ensure that C3b is deposited on appropriate surfaces.
E
4-8: Which of the following does not contribute to generating the diversity of antigen-binding specificities among immunoglobulins? A. somatic hypermutation B. random combination of heavy and light chains C. somatic recombination D. activation-induced cytidine deaminase (AID) E. alternative splicing of heavy-chain RNA transcripts.
E
6-8: All of the following are properties of B-1 cells except A. They exhibit polyspecifcity. B. They arise during fetal development. C. They express CD5 on their cell surface. D. They are commonly associated with the cause of chronic lymphocytic leukemia (CLL). E. They have extensive N nucleotide diversity in VDJ junctions.
E
6-9: Which of the following statements regarding negative selection of B cells is correct? A. Negative selection is a process that occurs in secondary lymphoid organs. B. Negative selection is a process that occurs in the bone marrow but not in secondary lymphoid organs. C. Negative selection ensures that B cells bearing receptors for pathogens that will not be encountered in a person's lifetime are eliminated to make room for B cells bearing useful receptors. D. Negative selection eliminates B cells at the end of an infection as a means of terminating an immune response once the pathogen has been removed from the body. E. Negative selection ensures that autoreactive B cells are prohibited from emerging in the body.
E
3-9: Identify the mismatched pair. A. MyD88: adaptor protein B. ICAM-1: LFA-1 C. chemokine receptor: G protein D. CD14: LPS E. NK cells: IFN-γ F. selectins: protein ligands.
F
3-12: Identify two ways in which IL-1β is regulated so as to minimize its destructive potential in the human body.
First, IL-1β is synthesized as an inactive precursor called proIL-1β, which is retained in the cytoplasm. It is activated only after cleavage by caspase 1. Second, caspase 1 is also made as an inactive precursor called procaspase 1. Upon macrophage activation and assembly of the inflammasome, procaspase 1 accumulates there as oligomers favoring the autoproteolysis of procaspase 1 to form caspase 1. Caspase 1 then facilitates the maturation of IL-1β in the cytoplasm and also in specialized secretory granules, and IL-1β is then subsequently secreted in large quantities by the macrophage.
4-13: Which of the IgG subclasses would you think was in principle most desirable for use as a therapeutic monoclonal anti- body, and why? Are there any disadvantages to using this subclass and how might they be overcome?
IgG4 would be considered the most desirable in principle because it lacks the ability to activate complement, and so will not trigger complement-mediated inflammation, which could cause damage to the patient. However, the monoclonal IgG4 will swap immunoglobulin chains with the patient's IgG4 at high frequency, thus becoming functionally monovalent, compromising its ability to bind as strongly to antigen as the other, stable, IgG subclasses. One solution would be to alter the CH3 region of IgG4 genetically in such a way that it cannot swap heavy:light chain units with other IgG4 antibodies but retains the inability to activate complement.
1-11: Explain how the adaptive and innate immune systems work together to generate an effective immune response.
In most cases, a prior innate response to infection is necessary for lymphocytes to be activated to produce an adaptive immune response. In the innate response, macrophages activated by pathogen-associated molecules release cytokines that promote inflammation, slow the spread of infection, and help activate an adaptive immune response in peripheral lymphoid organs.
6-13B: B-cell tumors originate during different developmental stages of B cells during their maturation in the bone marrow or after maturation and export to the periphery. B. How might the immunoglobulin expressed on pre-B-cell leukemia cells be different from that expressed on immature B cells?
Pre-B-cell leukemia is characterized by transformation before the rearrangement of light-chain genes. If transformation occurs at the large pre-B-cell stage, the immunoglobulin on the cell surface will be composed of ȝ:VpreBȜ5. If transformation occurs at the small pre-B-cell stage, there would be little or no immunoglobulin on the cell surface because surrogate light chain expression is turned of at this stage and the ȝ heavy chains are retained in the endoplasmic reticulum. Normal immature B cells that have not undergone transformation express IgM containing ȝ plus a ț or Ȝ light chain.
1-1B: What is the difference in function between primary and secondary lymphoid tissues, and what are the principal events that take place in each?
Primary (or central) lymphoid tissues are the anatomical locations where lymphocytes complete their development and reach the state of maturation required for the recognition of, and response to, a potential pathogen. B cells mature in the bone marrow and fetal liver, and T cells mature in the thymus. Both lymphocyte lineages are derived from a common hematopoietic stem cell. Secondary (or peripheral) lymphoid tissues provide the anatomical sites where lymphocytes encounter antigen and immune responses are induced. Antigen is delivered to the secondary lymphoid tissues through an afferent lymphatic vessel, and is retained in the lymphoid tissue or encounter with lymphocytes bearing antigen-specifc receptors.
3-6: Describe in chronological order the steps involved in the recruitment of neutrophils to infected tissue sites during an innate immune response. Use the following terms in your description: rolling adhesion, tight binding, extravasation, migration, infammatory mediators, integrins, adhesion molecules, chemokines, selectins, sialyl-Lewisx, and basement membrane proteases.
Step 1: dilation of blood capillaries, combined with the binding of neutrophil sialyl-Lewisx carbohydrate to selectins, a type of adhesion molecule, expressed on activated endothelium, slows down neutrophils as they roll along the endothelium, binding reversibly to the endothelial selectins, a process called rolling adhesion. Step 2: in response to the chemokine CXCL8 through binding to CXCR1 and CXCR2 chemokine receptors, the neutrophil integrins LFA-1 and CR3 increase their affinity for the endothelial adhesion molecules ICAM-1 and ICAM-2 through conformational changes. Neutrophils are now engaged in tight binding, are immobilized on the endothelium, and the rolling stops. Step 3: the neutrophil squeezes between the endothelial cells, a process known as extravasation. When the basement membrane is encountered, proteases (such as elastase) are secreted by the neutrophil causing degradation of the laminins and collagens of the basement membrane, and the process of extravasation is complete. Step 4: migration to the focus of infection is mediated through a CXCL8 gradient established by activated macrophages in the infected tissue. Neutrophils bearing CXCL8 receptors will travel toward the highest concentration of CXCL8 until they arrive at the focus of infection, and will also secrete their own CXCL8, which will assist with the migration of even more neutrophils to the infected location.
2-15: Jonathan Miller, aged 6 years, was brought to emergency room by his parents; he was presenting with fever, severe headache, a petechial rash, stiff neck and vomiting. Jonathan had a history of recurrent sinusitis and otitis media, all caused by pyogenic bacteria and treated successfully with antibiotics. Suspecting bacterial meningitis, the attending physician began an immediate course of intravenous antibiotics and requested a lumbar puncture. Neisseria meningitidis was grown from the cerebrospinal fluid. The physician was concerned about the recurrence of infections caused by pyogenic bacteria, and he suspected an immunodefciency. He ordered blood tests and found the serum complement profiles to have low C3, factor B, and factor H, and undetectable factor I. Which of the following explains why a factor I deficiency is associated with infections caused by pyogenic bacteria? A. Elevated levels of C3 convertase C3bBb interfere with the activation of the classical pathway of complement activation. B. Rapid turnover and consumption of C3 in the serum causes inefficient fixation of C3b on the surface of pathogens, compromising opsonization and phagocytosis. C. Factor I is an opsonin that facilitates phagocytosis. D. Factor I is a chemokine and is important for the recruitment of phagocytes. E. Factor I is required for assembly of the terminal components of the complement pathway.
The correct answer is B. In the absence of factor I, the alternative C3 convertase C3bBb is forming continuously, even in the absence of infection. This results in depletion of the C3 pool in the blood, lymph, and other extracellular fluids, lowering its concentration to levels below the threshold needed to mount effective innate immune responses that rely on the alternative pathway of complement activation. Encapsulated bacteria pose a particular threat because their eradication is dependent on opsonization, in which the opsonin C3b has a key role.
3-14: Two-year-old Jaxon Markowski presented with a hyperpigmented lacy rash on his torso. He had a history of recurrent bacterial infections, had been underweight for age since birth, and had frequent bouts of diarrhea and vomiting. He had a healthy 7-year-old sister and his mother had a stillbirth male baby 4 years ago. Jaxon's temperature runs higher than normal and he did not sweat. Closer examination revealed diffuse alopecia (thinning and absence of hair) and frontal bossing (protruding forehead). Jaxon's recently erupted front teeth were cone-shaped, and he exhibited periorbital wrinkling and darkening. Blood tests revealed an abonormally high white blood cell count, low IgG and IgA, and normal IgM concentrations. Flow cytometry showed low NK-cell numbers. Skin biopsy revealed difuse granulomatous inflammation and tested positive for Mycobacterium avium. Antibiotic combination therapy was begun and intravenous immunoglobulin (IVIG) was administered, to which Jaxon responded favorably. Molecular testing confirmed an insertion of cytosine at nucleotide 1167 in exon 10 of the X-chromosome encoded IKKγ gene (also known as NFțB essential modifier, or NEMO), causing a frameshift mutation affecting protein-protein interactions of the zinc-fnger domain. Jaxon's mother was confirmed as a heterozygous carrier. Which of the following best describes the consequence of this mutation? A. The respiratory burst is impaired in phagocytes owing to insufficient hydrogen peroxide production. B. NFțB is retained in the cytosol of macrophages in an inactive state in a complex with its inhibitor IțB. C. Increased susceptibility to lysis of red blood cells through unregulated assembly of the membrane attack complex. D. Loss of ability of macrophages to secrete cryptdins. E. Inability of host cells to synthesize IFN-α.
The correct answer is b. Mutations in NEMO (a subunit of IKK) compromise the activity of IKK, which is required for the phosphorylation of IțB and its subsequent release from NFțB in the cytosol. NFțB is thereby inhibited from translocating to the nucleus, where as a transcription factor it normally directs the synthesis of TNF-α and other inflammatory cytokines, as well as other proteins involved in development and immunity. Answer a is the consequence of a defect in NADPH oxidase causing chronic granulomatous disease. Answer c is associated with a defect in forming DAF, HRF, and CD59 as a result of the inability to form their GPI linkages. Paneth cells in the intestinal tract, not macrophages, make cryptdins, and their synthesis is independent of NFțB, so answer d is not correct. Finally, answer e is not correct because the expression of IFN-α is independent of NFțB and is regulated instead by interferon-response factor 7 (IRF7).
1-12: Two-year-old Janice Tumminello survived an episode of Haemophilus infuenzae septicemia at 4 months by intravenous antibiotic therapy. Her immunizations are up to date. Three days ago her adoptive parents became concerned when she became lethargic, had several bouts of vomiting, and developed a fever, and they took her to the emergency room. She had a rapid pulse and low blood pressure, her peripheral areas were cold, and purpura began to develop on her fingers and toes. Blood cultures tested positive for Streptococcus pneumoniae. Aggressive antibiotic treatment and fluid-replacement therapy were successful in preventing further dissemination of the bacteremia. However, amputation of three digits on the left hand and debridement of her toes on both feet was required. A diagnosis of overwhelming severe pneumococcal sepsis was made. DNA analysis showed that Janice had a deleterious mutation in a gene encoding _________, which is associated with congenital asplenia. A. an immunoglobulin B. a defensin C. a ribosomal protein D. a complement protein E. a T-cell receptor.
The correct answer is c. Congenital asplenia runs in families and results from insufficient production of the ribosomal protein SA, which is required for the spleen to develop. Janice inherited the defective gene from one of her natural parents. Infections with encapsulated bacteria such as Streptococcus pneumoniae, which are surrounded by a thick polysaccharide capsule and are resistant to phagocytosis, are particularly problematic in children with congenital asplenia, because the spleen is the lymphoid organ that filters the blood and prevents such bacteria from entering the bloodstream and causing sepsis. Defensin is one of many antimicrobial substances that defend epithelial surfaces, so its absence is unlikely to overwhelm host defenses, as seen in this case. A deficiency in immunoglobulin or T-cell receptor production, or the inability to activate complement, would cause a increased risk for a number of bacterial infections, not just encapsulated bacteria in the bloodstream, and numerous infections would have been observed in Janice since her birth if any of these proteins had not been functional.
4-15: Tree-week-old Xavier Capelleto was brought to the emergency room with a bright scaly rash that first developed on his legs and then spread to his trunk and face. He also had blisters on his palms and the soles of his feet. Xavier's parents said that he had been experiencing looser bowel movements than expected, a large amount of yellow pus had been accumulating around his swollen eyelids, and he showed signs of oral thrush. Tests revealed that Xavier's lymphocyte count was only 8% of total white blood cells (normal = 50%), all immunoglobulins were markedly decreased except for IgE, and no thymic shadow was detected on a chest X-ray. Eosinophilia was also detected. His parents were told that Xavier had an autosomal recessive form of severe combined immunodefciency (SCID) known as Omenn syndrome, which affects the development of both B cells and T cells. A bone marrow transplant was recommended; however, Xavier died from respiratory failure due to an opportunistic bacterial infection. This history is consistent with a genetic deficiency in A. α- or β-defensins B. activation-induced cytidine deaminase (AID) C. MHC class I D. RAG-1 or RAG-2 E. Toll-like receptors.
The correct answer is d. In the absence of functional RAG-1 or RAG-2, which are required for V(D)J recombination, the rearrangement of both immunoglobulin and T-cell receptor genes is impaired. This interferes with the normal development of B cells and T cells, accounting for the markedly lower number of lymphocytes in the total white blood cell count. Te diagnosis is supported by the absence of a thymic shadow on the chest X-ray, which would be visible if T-cell development were proceeding normally. AID deficiency would compromise immunoglobulin class switching and a hyper IgM syndrome would be expected. MHC class I deficiency would only affect the development of CD8 T cells because its expression on thymic epithelium is necessary for intrathymic maturation of CD8 T cells. Toll-like receptors and defensins have important roles in innate immune responses, but a deficiency of either would not explain the failure of B and T lymphocyte development.
2-14: John Binstead, 27 years old, has noticed that his urine was cola-colored in the morning for the past 5 days, and today he experienced a sudden onset of severe abdominal pain. Physical exam, blood tests, and urine analysis show that John is anemic as the result of intravascular hemolysis. A Coombs test is negative, ruling out autoimmune hemolytic anemia. Flow cytometric analysis of peripheral blood cells for CD235a (glycophorin A, present on erythroid precursors and mature red blood cells) together with CD55 (decay-accelerating factor) and CD59 (pro-tectin) reveals the absence of CD55 and CD59 on 54% of his red blood cells. Molecular analysis confirms a defective PIGA gene, which encodes the protein phosphatidylinositol glycan class A, which is involved in producing glycophosphatidylinositol anchors for many different proteins, including CD55 and CD59. John is diagnosed with paroxysmal nocturnal hemoglobinuria. A long-term treatment regimen including the administration of intravenous eculizumab, an anti-C5 humanized monoclonal antibody, is recommended. Which of the following provides the rationale for selecting eculizumab for the long-term management of John's condition? A. The inhibition of anaphylatoxins such as C5 decreases the inflammation that is responsible for hemolytic anemia. B. By blocking the activity of C5, the early events of complement will not be able to produce a functional C5 convertase. C. GPI anchors will form correctly if C5 is inhibited. D. A defect in CD59 function renders red blood cells especially susceptible to lysis if the membrane-attack complex is able to form. E. None of the above.
The correct answer is d. In the absence of the complement control protein CD59 (protectin), which normally prevents the recruitment of C9 by the complex of C5b, C6, C7, and C8 on human cells, the formation of the membrane-attack complex by all three complement pathways is not fully regulated, and the host cell is more susceptible to lysis. Because C5 must first be converted to C5b to initiate the formation of this complex, if C5 is blocked by eculizumab, then C5b will not be available, and the red blood cell surface will be spared from lysis. Option a is incorrect because it is C5a, not C5, that is an anaphylatoxin, and it is the formation of a transmembrane pore, not inflammation, that causes red cell lysis. Option b is incorrect because C5 convertase production does not require C5; C3b2Bb is the C5 convertase of the alternative pathway, and C4b2a3b is the C5 convertase of the lectin and classical pathways. Finally, option c is incorrect because GPI anchor formation is not inhibited by C5; normal individuals with functional C5 are able to form GPI anchors provided that the metabolic pathway for doing so is not defective, as is the unfortunate case for John Binstead.
4-16: Aliya Agassi, a 3-year-old girl with pneumonia, a temperature of 40.8°C, respirations 42 per minute (normal 20), and blood oxygen saturation of 90% (normal is more than 98%), was admitted to the hospital. Her neck and armpit lymph nodes were enlarged, and X-rays confirmed inflammation in the lower lobe of her right lung. Her medical history revealed two previous cases of pneumonia and six middle-ear infections that were treated successfully with antibiotics. A blood culture grew Haemophilus infuenzae. Blood tests showed elevated levels of IgM above normal, whereas IgA and IgG were not detected. Her father had normal levels of serum IgA, IgG, and IgM. Which of the following is the most likely cause of her symptoms? A. acute lymphoblastic leukemia B. IgA deficiency C. X-linked agammaglobulinemia D. severe combined immunodeficiency E. X-linked hyper IgM syndrome F. AID deficiency G. myeloma.
The correct answer is f. Aliya has IgM anti- bodies, so this is clearly not a case of X-linked agammaglobulinemia, in which a complete absence of immunoglobulin is expected. The father has normal immunoglobulin levels and the patient is a girl, so X-linked hyper IgM syndrome is highly unlikely. IgA deficiency can be ruled out because she does not also make IgG. Patients with acute lymphoblastic leukemia do not have an isotype-switching defect, and children with severe combined immunodeficiency die in their first year without treatment. A defect in both copies of the gene encoding activation-induced cytidine deaminase (AID) is most likely; AID is required for both isotype switching and somatic hypermutation, which accounts for Aliya's ability to make IgM but her inability to make any other antibody isotype. Both of her parents would be heterozygous carriers of the AID defect but would produce sufficient amounts of AID to escape immunodeficiency.
2-4: Explain why the type of innate immune response used by the host during an infection is dependent upon the particular location in which the pathogen resides.
The innate immune response must be of the appropriate form to access the particular compartment of an ongoing infection. If a pathogen exists in extracellular spaces or surfaces, then soluble molecules such as complement and antimicrobial peptides are effective in eradicating the pathogen. Some pathogens, however, reside in intracellular compartments, such as the nucleus, cytosol, or vesicles. If the pathogens are enclosed within a vesicle, the innate immune response instructs the infected cell to direct antimicrobial mechanisms to the interior of the vesicle to eradicate viable microbes. Macrophages carry out this type of antimicrobial activity. If the pathogens are replicating free in the nucleus or cytosol, then innate mechanisms are more aggressive and are aimed at killing the infected cell.
1-1A: Name the primary lymphoid tissues in mammals and the main types of secondary lymphoid tissue.
The primary (or central) lymphoid tissues are the bone marrow (and liver in the fetus) and the thymus. The main secondary (or peripheral) lymphoid tissues are the lymph nodes, spleen, and mucosa-associated lymphoid tissues (MALT). The last of these include gut-associated lymphoid tissue (GALT), such as the tonsils, adenoids, appendix, and Peyer's patches, and bronchial-associated lymphoid tissues (BALT).
