q25

When stimulated by binding to bacterial products, the fMet-Leu-Phe (fMLF) receptor triggers multiple responses by phagocytes, including migration and induction of antimicrobial activities. Most of these responses are activated by small GTPases of the Rac and Rho families that are indirectly activated by fMLF receptor stimulation. The fMLF receptor can initiate multiple downstream signaling pathways because: A. It couples to a heterotrimeric G protein that has and subunits with independent activities. B. It couples directly to two different guanine nucleotide exchange factors (GEFs). C. It binds to Rac, Rho, and cdc42 directly. D. It promotes fusion of phagosomes with lysosomes, initiating multiple signals. E. It induces assembly of multiple enzymes from individual cytosolic components.

A. It couples to a heterotrimeric G protein that has and subunits with independent activities.

NK cells can be activated following recognition of a virus-infected cell, if that cell has down-regulated expression of MHC class I proteins on its surface. However, NK cells can also recognize infected cells or tumor cells, even if they still express MHC class I proteins. In this latter case, activating receptors on NK cells are recognizing: A. Molecules on the target cell up-regulated by cellular or metabolic stress B. Cytokines secreted by the virus-infected or tumor cell C. MHC class I-like decoy molecules encoded by the virus D. Mutated self-proteins expressed by the tumor cell E. Double-stranded DNA in the cytoplasm of the infected or tumor c

A. Molecules on the target cell up-regulated by cellular or metabolic stress

Septic shock is a serious, often fatal response to an infection in the bloodstream. This response can be elicited in mice by intravenous injection of bacterial LPS. However, it was found that one strain of mice, C3H/HeJ, is resistant to LPS-induced shock. This fact was used to clone the gene for TLR-4 based on positional cloning from C3H-H3J mice. Another example of a strain of mice that is resistant to LPS-induced septic shock is: A. TNF-receptor-deficient mice B. TLR-2-deficient mice C. LFA-1-deficient mice D. Neutrophil-deficient mice E. Complement receptor-deficient mice

A. TNF-receptor-deficient mice

Adaptive immune responses are slow to develop, taking days to weeks after exposure to reach their peak. However, these responses are more specific than innate responses, and also generate immunological memory. These latter features, which provide enhanced protection upon re-infection with the same pathogen, are the basis of: A. Vaccines B. Antibiotics C. Systemic shock D. Complement activation E. Phagocytosis

A. Vaccines, vaccines are inactivated material put into a healthy individual to prevent re-infection with a live pathogen of the same

9. Some Pattern Recognition Receptors (PRRs) recognize nucleic acids, like RNA or DNA. Since our own cells contain human RNA and DNA, the activation of innate immune pathways by these PRRs must rely on additional criteria to discriminate self from nonself. Additional criteria include everything EXCEPT: A. The subcellular location of the RNA B. The presence of adenosine residues in viral RNA C. The methylation state of the DNA D. Unique structures found on viral DNA E. The subcellular location of the DNA

B. The presence of adenosine residues in viral RNA

Antibodies, complement proteins, and phagocytic cells provide effective protection against all of the following types of infections in Figure Q2.1, except: A. Fungi B. Virus-infected cell C. Worms D. Bacteria E. Viruses

B. Virus-infected cell

The antibody surface involved in antigen binding varies depending on the size and nature of the antigen. This surface can be concave or flat, and sometimes, can have extended protrusions. This is accomplished by: A. Flexibility in the hinge regions of the antibody allowing rotation of the antigen-binding sites B. Some antibodies using V region framework sequences instead of the CDRs to bind antigen C. The ability of different CDR sequences to form many structurally distinct shapes and surfaces D. The ability of the same heavy chain to pair with different light chains E. The differential usage of κ versus λ light chains, as κ chains form concave binding sites whereas λ chains make flatter surfaces

C. The ability of different CDR sequences to form many structurally distinct shapes and surfaces

An infant with recurrent bacterial and fungal infections is suspected to have an immunodeficiency disease. Within two days after exposure to a pathogen, the organisms have proliferated to dangerous levels requiring immediate systemic antibiotic treatment. It is unlikely that this infant has a defect in B or T lymphocyte responses to the infection because: A. Bacteria and fungi do not require B cell or T cell responses for their clearance. B. Bacteria and fungi are not efficiently transported to draining lymph nodes to initiate adaptive immune responses. C. Systemic infections of bacteria and fungi are usually cleared by the spleen. D. The defective immune response occurs too rapidly following infection to be due to a defect in B or T lymphocytes responses. E. Adaptive immune responses require dendritic cells to take up and degrade pathogens

D. The defective immune response occurs too rapidly following infection to be due to a defect in B or T lymphocytes responses.

Macrophages express multiple types of receptors on their surface that stimulate phagocytosis of microbes, leading to pathogen internalization and destruction. Many of these receptors, such as Dectin-1, rely on direct recognition of a PAMP on the pathogen surface. However, some receptors that stimulate phagocytosis rely on soluble factors (not associated with the phagocyte membrane) to identify and mark the pathogen for uptake by the phagocyte. One such receptor is: A. The mannose receptor B. The class A scavenger receptor C. The lipid receptor D. The macrophage C-type lectin receptor E. The complement receptor

E. The complement receptor

Individuals with defects in T cell development have a severe immunodeficiency disease called SCID (severe combined immunodeficiency disease). In these individuals, the absence of all T cells causes defects in both cell-mediated (T cell-based) and humoral (antibody-based) immune responses. The defect in antibody responses in SCID patients is due to: A. The important role of T cells in regulating B cell development in the bone marrow B. The inter-dependence of T cells and B cells for the normal development of secondary lymphoid organs. C. The absence of phagocytic cells needed for antibody-dependent pathogen clearance in SCID patients D. The poor survival of B cells in patients with defects in their T cells E. The important role of T follicular helper cells in generating protective antibody responses

E. The important role of T follicular helper cells in generating protective antibody responses

True/False: The classical and lectin pathways of complement activation converge at the step of C3 activation. However, the initiating steps of each pathway use protein components and enzymatic mechanisms that share no similarity with each other.

False

True/False: Innate lymphoid cells and NK cells are effector cells that respond rapidly after encountering a pathogen. Several different subsets of innate lymphoid cells exist, and each is specialized to respond to a category of pathogen (e.g., viruses, extracellular bacteria, helminthic parasites, etc). Innate lymphoid cells reside primarily in tissues such as the lungs, the lining of the gastrointestinal tract, and the skin, because these sites represent the major routes of entry of pathogens into the body.

True

What is the minimum number of amino acids that needs to change for a neutralizing antibody to the neuraminidase of the H1N1 strain on the left to no longer bind to the neuraminidase of the H1N1 strain on the right?

One substitution of amino acid would make it so the neuraminidase of the H1N1 on the left would no longer bind to the neuraminidase of the H1N1 on the right.

Short answer: Most B and T lymphocytes in the circulation appear as small, inactive cells, with little cytoplasm, few cytoplasmic organelles, and nuclei containing condensed inactive chromatin. Yet these cells comprise the adaptive immune response, without which individuals die in infancy. What is the explanation for this apparent dichotomy?

These cells are necessary for the adaptive immune response, however they will remain naïve unless they come into contact with a specific pathogen, and therefore useless to immune response. Only after coming into contact with the specific pathogen they are suited for will they proliferate to the immune response and be able to defend against pathogens. It is necessary that they must be activated

Short answer: A common mechanism by which sensor cells in the host detect micro-organisms relies on the production of unique microbial components not found in the host. Propose a strategy by which a clever microbe could evade this type of response.

To evade this response, a microbe could just change the cell wall or outer membrane so that the sensor cell receptors would not be able to recognize the newly developed microbe.

True/False: Antibody binding to a pathogen surface is greatly enhanced when both antigen-binding sites of the antibody are engaged at once, a feature known as bivalent binding. It is possible for antibodies to bind bivalently to a wide variety of components on many different pathogen surfaces due to the flexibility in the protein at the hinge region and at the V-C junction.

True

True/False: Dendritic cells are tissue resident myeloid cells that are highly phagocytic, like macrophages. However, dendritic cells do not play a major role in large-scale pathogen destruction; instead, they are important in initiating adaptive immune responses of T cells.

True

True/False: Each family of NK cell receptors has members that promote NK cell activation, and members that send inhibitory signals when engaged. The difference between activating and inhibitory receptors lies in their association with accessory proteins that promote downstream signaling, or in their ability to recruit and activate inhibitory phosphatases, respectively.

True

True/False: For cells of the innate immune system, each individual cell has multiple pattern recognition receptors, and can recognize many different pathogens. In contrast, cells of the adaptive immune system each express only a single antigen receptor, and have a single specificity for pathogen recognition.

True

True/False: MHC class I molecules generally bind peptides that are 8-10 amino acids. Each allelic variant has preferences for the amino acid residues at key anchor positions, but will not bind every possible peptide containing the correct anchor residues.

True

True/False: Neutrophils regulate the production of active cathelicidins (a class of antimicrobial peptides) by segregating the inactive propeptide from the processing enzyme that cleaves and activates it in two different types of cytoplasmic granules. These two types of granules are induced to fuse with phagosomes after ingestion of microbes, bringing the processing enzyme and the propeptide together.

True

True/False: Several pathogens produce proteins, either membrane-bound or secreted, that inactivate C3b that might be deposited on the pathogen surface. C3b is specifically targeted due to its central position in all three complement pathways.

True

True/False: T cells expressing : TCRs are distinct from those expressing : TCRs in that they do not generally recognize host cell responses to infections or tissue damage; rather they recognize components of the pathogen directly.

True

True/False: TH1, TH2, TH17, and T follicular helper (TFH) cells represent four different subsets of CD4 effector cells. Each of these subsets produces a distinct set of cytokines when stimulated, that in turn, act to mobilize distinct immune effector mechanisms. While TH1, TH2, and TH17 cells recruit and activate innate immune cells, TFH cells act to amplify the adaptive immune response.

True

True/False: The C3 convertase of the alternative complement pathway amplifies the overall magnitude of complement activation regardless of which of the three pathways initiated the complement activation initially.

True

True/False: The extravasation of neutrophils into tissues at sites of infection or inflammation requires changes to both the endothelium and to the neutrophil that are induced by chemokines and cytokines produced in the infected tissue.

True

True/False: The inflammatory response is characterized by four classic symptoms: heat, redness, pain, and swelling. In some instances, this response can be triggered by stimuli that are non-infectious such as asbestos, a process known as 'sterile inflammation.' When exposure to the stimulating trigger is persistent, a state of chronic inflammation can result. This process is likely to be detrimental to the health of the host.

True

When macrophages in a tissue encounter bacteria, they release cytokines that induce an inflammatory response. These cytokines act on other immune cells, to recruit them to the site of infection and to enhance their activities. In addition, these cytokines act on the endothelial cells of the blood vessel wall to: A. Increase their permeability, allowing fluid and proteins to leak into the tissue B. Solidify the tight junctions to prevent the bacteria from entering the blood C. Proliferate, allowing the blood vessel to enlarge D. Up-regulate microbicidal mechanisms, so they can kill bacteria E. Secrete anti-microbial peptides

A. Increase their permeability, allowing fluid and proteins to leak into the tissue

Chemokines such as CXCL8 have a key role in the rapid recruitment of neutrophils to the site in the tissue containing the focus of an infection. In this response, CXCL8 has two different functions. In addition to inducing integrin activation on the neutrophil, CXCL8 also functions to: A. Induce directional migration of the neutrophil in the tissue B. Induce increased expression of P-selectin and E-selectin on the endothelium C. Induce increased expression of integrins on the neutrophil surface D. Induce blood vessel dilation and fluid leakage into the infected tissue E. Induce increased phagocytic activity by the neutrophil

A. Induce directional migration of the neutrophil in the tissue

Once expressed on the surface of host cells, an MHC protein remains stably associated with its bound peptide for several days. This highly stable peptide binding behavior is important because: A. It prevents peptide exchanges on the cell surface, ensuring that peptide:MHC complexes are reliable indicators of the proteins present inside that host cell. B. If the MHC protein lost its peptide it would become unstable, and would be rapidly internalized and degraded. C. Pathogens would otherwise evade the immune response by making decoy peptides that mimic host cell peptides. D. Pathogens would be able to evade the T cell response by making proteases that cleave MHC proteins inducing peptide release. E. Immune responses to infection often induce noxious chemicals that damage surface MHC proteins, and might result in peptide loss.

A. It prevents peptide exchanges on the cell surface, ensuring that peptide:MHC complexes are reliable indicators of the proteins present inside that host cell.

The pattern recognition receptors on cells of the innate immune system are genetically encoded, meaning that their sequences and specificities are determined prior to the development of the individual. In contrast, the antigen receptors of B and T lymphocytes arise from a random rearrangement process that occurs differently in each lymphocyte as it develops. One potential problem entailed by the random process that generates lymphocyte antigen receptors is the possibility that: A. Some antigen receptors might recognize the individuals on cells or antigens B. Many lymphocytes might generate antigen receptors that don't recognize anything C. Many lymphocytes might generate antigen receptors that recognize multiple different pathogens D. Some antigen receptors might recognize foreign tissues and lead to graft rejection during organ transplantation E. Some lymphocytes might not generate functional antigen receptor proteins

A. Some antigen receptors might recognize the individuals on cells or antigens

Stimulation of the nucleic acid sensing TLRs that reside in endosomal membranes induces the production of a different cytokine response than is produced by stimulation of the plasma membrane TLRs. In part, this distinction is based on the different adapter proteins used by the nucleic acid sensing TLRs, leading to the activation of IRF factors. The cytokine response following stimulation of nucleic acid-sensing TLRs is characterized by production of: A. The antiviral cytokine, type I interferon B. TNF-, which induces increased vascular permeability C. Antimicrobial peptides by macrophages D. Chemokines that recruit neutrophils E. The inflammatory complement fragments, C3a and C5

A. The antiviral cytokine, type I interferon

The importance of complement activation as an innate immune defense against infections is illustrated by: A. The evolution of complement avoidance strategies by many pathogens B. The large number of proteins involved in the complement pathway C. The large number of complement regulatory pathways expressed by the host D. The existence of three different mechanisms for initiating complement activation E. The ability of the membrane attack complex to lyse some pathogens

A. The evolution of complement avoidance strategies by many pathogens

One surprising aspect of the immune system is that individuals make responses to human tissues from a different individual, causing serious problems for organ and tissue transplantation. The basis for this immune response is: A. The extensive polymorphism of MHC genes in the human population B. The fact that transplanted tissues often carry infectious microbes into the recipient C. The fact that individuals may differ in their blood group antigens (i.e., their blood type) D. The presence of many antigen-presenting-cells in the transplanted tissue E. The presence of many B and T lymphocytes in the transplanted tissue

A. The extensive polymorphism of MHC genes in the human population

The majority of vaccines work by eliciting pathogen-specific antibodies that circulate in our bodies and protect us in the event that we are later exposed to that specific pathogen. For most viruses and bacterial toxins that we are vaccinated against, these pre-existing antibodies are protective because: A. They neutralize the virus or toxin, preventing it from attaching to and entering our cells. B. They bind to the virus or toxin and carry it to the liver where it can be degraded. C. They bind to the virus or toxin and directly induce lysis. D. They induce mucus production that helps flush the toxin or virus out of the body. E. They bind to epithelial cells and induce the production of antimicrobial peptides.

A. They neutralize the virus or toxin, preventing it from attaching to and entering our cells.

Hepatitis C is a virus that infects hepatocytes, which are non-immune cells of the liver. Currently, patients with chronic Hepatitis C infections are treated with repeated administration of type I interferon, predominantly interferon . One aspect of this treatment that might aid the patient's immune system in clearing this virus infection is: A. Up-regulation of MHC class I expression levels on hepatocytes B. Activation of macrophages to produce noxious compounds that might kill the virus C. Induction of an inflammatory response to promote neutrophil trafficking to the liver D. Production of TNF- in response to type I interferon leading to vasodilation in theliver E. Induction of IL-1 and IL-6 leading to the acute phase response

A. Up-regulation of MHC class I expression levels on hepatocytes

Vaccination against many infectious diseases has provided enormous benefit in developed countries, leading to the virtual eradication of diseases such as polio, measles, smallpox, and others. However, efforts to create long-lasting vaccines against some viral infections, like Influenza and HIV, have not been successful to date because: A. Viruses like HIV and Influenza undergo antigenic variation to evade previous immune responses. B. Viruses like HIV and Influenza spread too rapidly in the population for a vaccine to be effective. C. Viruses like HIV and Influenza have RNA, rather than DNA genomes, and are resistant to current vaccine strategies. D. Viruses like HIV and Influenza infect via mucosal surfaces, a route that is not wellprotected by current vaccine strategies. E. Viruses like HIV and Influenza are transmitted vertically (from mother to child) during fetal development, so babies are infected before they can be vaccinated.

A. Viruses like HIV and Influenza undergo antigenic variation to evade previous immune responses.

The cellular distribution of MHC class I versus MHC class II molecules is quite different, with MHC class II molecules generally expressed on a very limited set of cell types. This is because: A. It would be detrimental to have CD8 T cells killing macrophages or B cells. B. CD4 T cells generally secrete cytokines that act on macrophages and B cells. C. Viruses generally do not infect and replicate in macrophages and B cells. D. Dendritic cells are more important in stimulating CD4 than CD8 T cell responses. E. CD4 T cells can only kill macrophages, dendritic cells, and B cells.

B. CD4 T cells generally secrete cytokines that act on macrophages and B cells.

Many of the inflammatory mediators produced by tissue macrophages at sites of infection act on the endothelial cells lining the blood vessel walls. An exception to this is (are) the: A. Cytokines that induce increased vascular permeability B. Chemokines that induce directed migration of blood monocytes C. Cytokines that induce increased expression of adhesion molecules D. TNF produced by tissue-resident sensor cells E. Bradykinin produced that causes pain

B. Chemokines that induce directed migration of blood monocytes

Amino acid sequence analysis of all of the peptides found in a single IgG antibody would reveal unique peptide sequences totaling ~600-700 amino acids. Using this estimate, the predicted molecular weight of an antibody protein would be ~70-75 kDa. Yet, an intact antibody protein has a molecular weight of ~150 kDa. The explanation for this discrepancy is: A. IgG antibodies have many more heavy amino acids in them than most other proteins. B. Each IgG antibody is a complex of two identical light chains and two identical heavy chains. C. IgG antibodies tend to aggregate together during purification, thereby distorting molecular weight estimates. D. Each IgG antibody is a complex of four identical polypeptides .E. IgG antibodies are produced as dimers of two identical IgG monomers

B. Each IgG antibody is a complex of two identical light chains and two identical heavy chains.

The antigen receptor on a T cell recognizes a degraded fragment of a protein (i.e., a peptide) bound to a specialized cell surface peptide-binding receptor called an MHC molecule. One key aspect of this system is that the peptides displayed on MHC molecules can be derived from intracellular proteins. This mode of antigen recognition is particularly important in allowing the adaptive immune response to detect infections by: A. Large helminthic parasites in the gastrointestinal tract B. Intracellular pathogens, such as viruses and some protozoa C. Extracellular bacteria that colonize the lungs D. Fungi that form hyphae in the bronchial airways E. Fungal infections in the skin epithelium

B. Intracellular pathogens, such as viruses and some protozoa

Two strains of mice were infected with 5x104 PFU of Influenza A virus, and the survival data shown in Figure Q3.31 were obtained. Next, both strains were infected again with Influenza A, and levels of type I interferons (IFN-a and IFN-b) were measured and found to be similar between the two strains. Likewise, cells from both strains expressed similar levels of the IFN alpha/beta receptor (IFNAR). Which of the following proteins might be more highly expressed in strain B than in strain A following Influenza A infection? A. MHC class I B. Mx-1 C. TLR4 D. Complement C3 E. ICAM-1

B. Mx-1

Epithelial surfaces provide the first line of defense against infection by the use of several types of mechanisms. One of the chemical mechanisms used by epithelia is: A. Joining of epithelial cells by tight junctions B. Secretion of antimicrobial peptides by epithelial cells C. Production of mucus, tears, or saliva in the nose, eyes, and oral cavity D. Movement of mucus by cilia E. Peristalsis in the gastrointestinal tract

B. Secretion of antimicrobial peptides by epithelial cells`

Several subsets of innate lymphoid cells (ILCs) have been identified that share their patterns of cytokine production with the known subsets of T cells. The combined activity of related ILC and T cell subsets is effective in eradicating pathogenic infections because: A. ILCs cannot kill the pathogen, whereas the antigen-specific T cells can kill the pathogen. B. The early response of ILCs that reside at the site of infection is followed by the later more robust response of pathogen-specific T cells that migrate to the site of infection. C. The ILCs activate B cells to induce antibody responses whereas the T cells are able to directly eliminate the pathogen. D. The ILCs are induced to migrate from the site of infection to the draining lymph nodes where they activate the antigen-specific T cells. E. The ILCs are activated to secrete antimicrobial compounds which cause them to lyse, releasing RNA and DNA that act on T cells to stimulate T cell cytotoxic activities.

B. The early response of ILCs that reside at the site of infection is followed by the later more robust response of pathogen-specific T cells that migrate to the site of infection.

Inherited immunodeficiency diseases result from a single gene defect in one component of the immune system. By identifying the class of microbial pathogens a given immunodeficient individual becomes susceptible to, studies of these diseases indicate: A. Which type of antibiotics each patient should be given B. The essential immune mechanism required for resistance to each category of pathogen C. Whether the disease is a genetically inherited or an acquired form of immunodeficiency D. Whether the immunodeficiency disease is likely to be transmitted to another individual E. Whether the disease is likely to be life-threatening or not

B. The essential immune mechanism required for resistance to each category of pathogen

Multiple pathways for regulating complement activation limit the potential damage caused by complement deposition on host cells or caused by the spontaneous activation of complement proteins in the plasma. Genetic deficiencies in these mechanisms often lead to chronic inflammatory diseases, but in some cases can paradoxically lead to increased susceptibility to bacterial infections. This latter outcome may occur because: A. Complement regulatory proteins have dual functions in inhibiting and promoting complement activation. B. Uncontrolled complement activation leads to the depletion of serum complement proteins. C. The inhibition of the membrane attack complex by complement regulatory proteins normally leads to enhanced activation of the early steps of the complement pathway. D. Complement regulatory proteins normally cause the rapid depletion of plasma complement factors. E. Uncontrolled complement activation recruits the majority of phagocytic cells, leaving few remaining to fight infections in the tissues.

B. Uncontrolled complement activation leads to the depletion of serum complement proteins.

Individuals or mice with defects in the biochemical pathways needed for loading peptides onto MHC molecules show greatly increased susceptibility to virus infections. Experiments examining the MHC molecules present on the surface of host cells in these individuals would show: A. Normal numbers of MHC molecules expressed on host cells, but no peptides bound to them. B. Very low levels of total MHC proteins expressed on the cell surface. C. Normal numbers of MHC proteins on the surface but all of them bound to self-peptides not pathogen peptides. D. Very high levels of total MHC proteins expressed on the cell surface. E. Only virus-infected cells expressing high levels of MHC proteins on the cell surface.

B. Very low levels of total MHC proteins expressed on the cell surface.

To identify genes encoding the receptors for the cytokines IL-2, IL-4, and IL-7, an siRNA screen is performed using purified T lymphocytes. To identify siRNAs that knock-down cytokine receptor expression, the T cells have been transfected with a construct that produces green fluorescent protein (GFP) when any one of these three cytokines is used to stimulate the cells. When the screen is completed, several different siRNAs have been identified that substantially reduce the T cells ability to respond to these cytokines as shown in Figure Q3.22. A correct statement regarding these data is: A. siRNA-1 and siRNA-3 target subunits of the IL-2 receptor but siRNA-2 does not. B. siRNA-2 targets a shared subunit of all three receptors, whereas siRNA-1 and siRNA-3 donot. C. siRNA-3 targets a subunit of the IL-7 receptor, but the other two siRNAs do not. D. siRNA-2 and siRNA-3 do not target a subunit of the IL-2 receptor. E.siRNA-2 targets a subunit shared by all receptors in the hematopoietin receptor superfamily

B. siRNA-2 targets a shared subunit of all three receptors, whereas siRNA-1 and siRNA-3 donot.

Many different NOD-like receptors, including several with pyrin domains and several with HIN domains, can function to trigger inflammasome assembly leading to the activation of caspase-1. The reason for many different sensors in this innate response system is that: A. Each NOD-like receptor is expressed in a different set of phagocytic cells, depending on its tissue location. B. Each NOD-like receptor resides in a different intracellular compartment. C. Each NOD-like receptor performs a different step in the multi-step cascade leading to inflammasome activation. D. Each NOD-like receptor binds to a different adapter protein and triggers a different formof the inflammasome. E. Each NOD-like receptor recognizes different PAMPs and is activated by different pathogens

C. Each NOD-like receptor performs a different step in the multi-step cascade leading to inflammasome activation.

NK cells express receptors from several families, each of which has multiple members. Some of these receptors are activating and others are inhibitory, and NK cell activation is dependent on the balance of signaling overall. The individual NK cells in an individual: A. Always express a majority of activating versus inhibitory receptors B. Are more potent effectors of cytotoxicity than of cytokine-production C. Each express only a subset of all possible NK receptors D. Are not considered members of the innate lymphoid cell lineage E. Undergo massive proliferation in response to infection, similar to T lymphocytes

C. Each express only a subset of all possible NK receptors

Even when the complement cascade fails to proceed beyond generating the C3 convertase, complement activation is effective at inducing pathogen uptake and destruction. This process of immune protection is mediated by: A. Activation of complement inhibitory receptors on phagocytes that promote pathogen uptake B. Activation of soluble proteases in the serum that disrupt pathogen membranes C. Engagement of complement receptors on phagocytes by C3b and its cleavage products which promotes phagocytosis D. Engagement of complement receptors on B cells that promotes antibody production E. Stimulation of antimicrobial peptide secretion by phagocytes

C. Engagement of complement receptors on phagocytes by C3b and its cleavage products which promotes phagocytosis

Lymph nodes function as meeting points between antigen-bearing dendritic cells arriving from the tissue and recirculating B and T lymphocytes. Whereas the dendritic cells coming from the tissue enter the lymph node via the afferent lymphatic vessels, the recirculating lymphocytes enter the lymph node: A. Also from the lymph fluid draining the tissue B. Directly from their primary lymphoid organ where they develop C. From the blood by crossing the high endothelial venules D. By being trapped in the lymphoid follicle by resident macrophages E. By being carried there by dendritic cells

C. From the blood by crossing the high endothelial venules

Unlike B lymphocytes, T lymphocytes do not generate a secreted form of their antigen receptor after they are activated and proliferate. This is because the effector functions of T cells are restricted to: A. Responses important in protozoan infections, but not other types of infections B. Interactions with large helminthic parasites, which cannot be phagocytosed C. Interactions with other cells, such as virus-infected cells or other immune cells D. Responses important in mucosal surfaces (e.g., the lung), where antibodies cannot go E. Stimulating B cells and not any other types of cells

C. Interactions with other cells, such as virus-infected cells or other immune cells

The skin and bodily secretions provide the first line of defense against infection. One response in this category that is common during upper respiratory virus infections is: A. Production of antibodies B. Infiltration by white blood cells C. Mucus production D. Increased saliva production E. Fever

C. Mucus production

The drawing in Figure Q4.12 shows antibodies bound to repetitive epitopes on the surface of a bacterial pathogen. Even though all of these epitopes are identical, not all of them have antibodies bound to them. The most likely explanation for this failure of antibodies to bind to every possible epitope on the surface of the pathogen is: A. There is an insufficient amount of antibody to saturate all the epitopes B. The pathogen has an immune evasion strategy to avoid antibody binding to all epitopes C. Some of the epitopes cannot bind antibody due to steric hindrance. D. The antibodies are only able to bind when both antigen-binding sites are engaged on the pathogen surface. E. The epitopes on the pathogen are not all in the same conformation, so not all will bind the same antibody.

C. Some of the epitopes cannot bind antibody due to steric hindrance.

Cytokine receptors of the hematopoietin superfamily engage signaling pathways that begin with JAK kinases and lead to activation of STAT-family transcription factors. Each receptor subunit in this superfamily binds a specific JAK kinase (one of four members) and each receptor complex usually activates one major STAT homodimer (one of seven). The specificity for activation of one STAT homodimer by each cytokine is determined by: A. The specificity of each JAK kinase for only phosphorylating one or two out of the seven possible STAT members B. The specificity of each cytokine receptor complex to only activate one of the four Jak kinase members, which then homodimerizes C. The amino acid sequence surrounding the phosphorylated tyrosine on each cytokine receptor subunit's cytoplasmic tail D. The expression of only one STAT member in each type of immune cell, depending on which cytokine receptors are expressed E. The inhibition of all but one STAT protein by the inhibitor SOCS proteins expressed in each cell type

C. The amino acid sequence surrounding the phosphorylated tyrosine on each cytokine receptor subunit's cytoplasmic tail

The best evidence supporting the concept of immunological memory is: A. The increased numbers of antigen receptors expressed by lymphocytes after primary exposure to an antigen B. The increased levels of cytokines made by lymphocytes after primary exposure to an antigen C. The increased rapidity and magnitude of the secondary response to the same antigen D. The increased swelling of lymph nodes during the secondary response to the same antigen E. The long lifespan of vertebrates, which would be impossible without immunological memory

C. The increased rapidity and magnitude of the secondary response to the same antigen

Dendritic cells in the skin, known as Langerhans cells, express very high levels of the NOD-like receptor, NLRP3. Previous studies showed that treatment of these cells with the Staphylococcus aureus pore-forming toxin causes K+ efflux from the cells. To investigate whether this signal could induce IL-1 (an inflammatory cytokine) secretion by the cells, the following study (Figure Q3.16) was performed: The explanation for these results is: A. NLRP3 is not activated by K+ efflux from the cells. B. The S. aureus toxin does not kill the Langerhans cells. C. The live S. aureus bacteria activate a TLR and NLRP3. D. The S. aureus membrane prep does not contain a TLR ligand. E. TLR activation by S. aureus membranes induces interferon production.

C. The live S. aureus bacteria activate a TLR and NLRP3.

The first pattern recognition receptor (PRR) important in innate immune responses was discovered in the fruit fly Drosophila melanogaster. Stimulation of this receptor, called Toll, induces: A. The synthesis of prostaglandins and leukotrienes B. The inflammatory response in Drosophila hemolymph vessels C. The production of antimicrobial peptides D. The recruitment of phagocytic cells to the site of infection E. The activation of Drosophila complement

C. The production of antimicrobial peptides

The formation of the C3 convertase is a key step in complement activation that occurs in all three complement pathways. This enzyme cleaves C3 in blood plasma, leading to a conformational change in the C3b fragment that exposes its reactive thioester group. The activated C3b is potentially harmful to the host, if it becomes covalently attached to a host cell, rather than to the surface of a pathogen. This deleterious outcome is largely avoided by: A. The inability of active C3b to diffuse away in the blood plasma. B. The inability of active C3b to covalently attach to the membranes of eukaryotic cells. C. The rapid hydrolysis of active C3b in solution, rendering it inactive. D. The tight binding of active C3b to the C3 convertase. E. The ability of active C3b to recruit phagocytic cells.

C. The rapid hydrolysis of active C3b in solution, rendering it inactive.

Naive B and T lymphocytes are small, quiescent cells with little cytoplasm and low metabolic activity. Yet within hours after being activated following encounter with their antigen, these cells enlarge and up-regulate many biosynthetic and metabolic pathways. Approximately one day later, the cells begin dividing, and for several days they are the most rapidly dividing cells in the body, undergoing 2-4 rounds of cell division every day. In order to maintain this phenomenal rate of cell division, lymphoblasts must: A. Use the large energy stores accumulated by them when they were naive quiescent cells prior to their activation B. Engulf their neighboring small quiescent lymphocytes in order to take their lipids and proteins for raw material C. Up-regulate synthesis of mRNA and proteins, some of which encode for glucose transporters and enzymes used for glycolysis D. Phagocytose extracellular proteins and lipids and degrade them for energy production E. Macropinocytose metabolites and sugars from the blood for use in glycolysis

C. Up-regulate synthesis of mRNA and proteins, some of which encode for glucose transporters and enzymes used for glycolysis

Most normal tissues contain resident macrophages, and connective tissue sites in the gastrointestinal tract and the lung contain large numbers of these cells. Yet the blood also contains a high number of circulating 'classical' monocytes that can differentiate into macrophages after entering tissues. These circulating monocytes function to: A. Phagocytose and kill pathogens in the blood B. Line the endothelial surfaces of the blood vessels with phagocytic cells C. Enter lymph nodes and patrol for infecting microbes in these organs D. Amplify the local innate immune response by entering tissues that are infected E. Differentiate into dendritic cells during an inflammatory response

D. Amplify the local innate immune response by entering tissues that are infected

Immunodeficiency diseases occur when individuals have defects in leukocyte adhesion to inflamed endothelial cells, thereby impeding the extravasation of phagocytes into infected tissues. When neutrophils from one class of these patients were isolated and tested using in vitro assays for neutrophil-endothelial cell interactions and extravasation, it was found that the neutrophils could slowly roll along the endothelial vessel wall but were unable to arrest and migrate across the endothelium. The most likely protein deficient in these neutrophils is: A. ICAM-1 or ICAM-2 B. P-selectin C. E-selectin D. An integrin E. Sulfated sialyl-Lewisx

D. An integrin

Innate lymphoid cells (ILCs) are effector calls that generally reside in barrier tissues, such as the skin, the gut, and the lung. These cells closely resemble subsets of T lymphocytes, but lack a T cell antigen-receptor. Instead, these cells produce their effector molecules following stimulation by: A. Microbial PAMPs that stimulate pattern recognition receptors on ILCs B. TNF-a, which is produced during the inflammatory response C. Acute phase response proteins produced in the liver during an infection D. Cytokines made by other innate cells, such as macrophages or dendritic cells E. Antimicrobial peptides made by epithelial cells in response to infection

D. Cytokines made by other innate cells, such as macrophages or dendritic cells

One form of anemia results when individuals have a deficiency in the enzyme phosphatidylinositol glycan A (PIGA). This enzyme is required for the membrane attachment of proteins anchored by glycolipids to the plasma membrane, using what is called a 'GPI-linkage.' Included in the group of GPI-linked cell surface proteins is DAF/CD55. These individuals become anemic because: A. DAF/CD55 prevents the lysis of red blood cells by infecting pathogens. B. DAF/CD55 normally prevents the spleen from clearing healthy red blood cells from the circulation. C. In the absence of PIGA, the red blood cell membrane is bare of proteins allowing increased access of complement activating proteins to attach to the cell membrane. D. DAF/CD55 is a complement inhibitory protein that inactivates any C3 convertase that may form on host cell surfaces. E. In the absence of PIGA, red blood cells are unable to synthesize high levels of hemoglobin.

D. DAF/CD55 is a complement inhibitory protein that inactivates any C3 convertase that may form on host cell surfaces.

In patients with lymphomas, the cancer cells invade the bone marrow and destroy the environment required for normal hematopoiesis. This leads to bone marrow failure, which disrupts the production of hematopoietic cell lineages. All of the following cell types would be affected by this EXCEPT: A. Red blood cells B. Macrophages C. Lymphocytes D. Endothelial cells E. Granulocytes

D. Endothelial cells, because they make up our blood vessels

One striking feature of TCR interactions with peptide:MHC complexes is that amino acid residues in the MHC protein are as important to the TCR binding strength as are amino acid residues in the pathogen-derived peptide. This feature is in contrast to antigen recognition by antibodies, which is a direct interaction that is independent of other host proteins. Based on the different functions of T cells versus antibodies in the adaptive immune response, the fact that TCRs recognize components of both the MHC and the bound peptide exists to: A. Prevent TCRs from binding only to surface exposed epitopes of native pathogens B. Prevent immune evasion by a pathogen that has mutated the sequences required for antibody recognition C. Put constraints on T cell recognition, due to the potentially damaging effector molecules made by activated T cells D. Ensure that TCRs are focused on recognizing antigens associated with host cells, and not those that are free in solution E. Ensure that the pathogen has already been destroyed by the host cell before the T cell will recognize it

D. Ensure that TCRs are focused on recognizing antigens associated with host cells, and not those that are free in solution

The mucosal tissues of the body have their own unique set of immune structures that function as sites for initiating adaptive immune responses. The necessity for mucosa-associated lymphoid tissues to have unique cell types (M cells) and structures is because: A. The mucous layer lining mucosal surfaces makes it difficult for normal antigen-presenting cells to function. B. The epithelial surfaces that line the gut, lungs, and nasal passages prevent antigen-presenting cells from accessing microbes and microbial products. C. The epithelial cells found in mucosal tissues are distinct from those that provide barrier functions to the skin. D. Mucosal sites, where most pathogens access the body, are exposed to vast numbers of diverse microbes. E. Mucosal tissues lack innate sensor cells that can respond to PAMPs and provide short-term innate immune protection

D. Mucosal sites, where most pathogens access the body, are exposed to vast numbers of diverse microbes.

Mycobacteria are intracellular pathogens that have adapted to life inside phagocytic cells, such as macrophages. These intracellular bacteria are taken up by phagocytosis, similar to other pathogens, but the bacteria are not killed. One possible mechanism that could account for this immune evasion by mycobacteria is their ability to: A. Prevent induction of nitric oxide production in the phagosome B. Prevent the acidification of phagosomes C. Prevent the expression of antimicrobial peptides in the phagosome D. Prevent fusion of phagosomes with lysosomes E. Kill the macrophage before it kills them

D. Prevent fusion of phagosomes with lysosomes

The innate immune response together with antibodies are generally not effective at clearing infections established by pathogens that replicate inside host cells. The evolution of T cells has provided a means for the immune response to 'see' intracellular infections based on the ability of T cells to: A. Secrete cytokines that diffuse into the infected tissue B. Activate type I interferon production by macrophages and dendritic cells C. Activate macrophages to induce inflammation D. Recognize pathogen-derived peptides on host MHC surface molecules E. Express cytoplasmic sensors for detecting pathogen-derived nucleic acids

D. Recognize pathogen-derived peptides on host MHC surface molecules

Antibody heavy and light chain polypeptides consist of repeated domains, each of which is ~110 amino acids and folds up into a compact three-dimensional structure known as an 'immunoglobulin domain.' These immunoglobulin domains are: A. Mixed and matched between different antibody heavy and light chains to produce variability B. Always identical to each other within a single antibody heavy chain or light chain polypeptide C. Always differ in amino acid sequence between different light chain polypeptides in both of the two light chain immunoglobulin domains D. Similar but not identical in amino acid sequence when comparing the domains in a single heavy chain polypeptide E. Identical in amino acid sequence for every domain when comparing different antibody heavy chain polypeptides to each other

D. Similar but not identical in amino acid sequence when comparing the domains in a single heavy chain polypeptide

In recent years, several new vaccines have been developed that are made frompurified viral surface proteins, rather than intact or live viruses. They are referred to as subunit vaccines. In order to generate a protective adaptive immune response to a subunit vaccine, the viral protein(s) must be mixed with an adjuvant. The adjuvant functions to: A. Mimic the process of normal virus entry by binding to the host receptor and inducing receptor-mediated endocytosis B. Induce vascular permeability to promote the accumulation of fluid and serum proteins at the vaccine injection site C. Induce the production of chemotactic proteins that recruit neutrophils and then monocytes to the site of vaccine injection D. Stimulate dendritic cells to up-regulate co-stimulatory molecules and migrate to the regional lymph node E. Promote the activation of the complement cascade to induce complement deposition on the viral subunit proteins

D. Stimulate dendritic cells to up-regulate co-stimulatory molecules and migrate to the regional lymph node

Some species, like camels, alpacas, and llamas, have evolved variant forms of immunoglobulin proteins that retain the ability to bind to antigens. While overall the antibodies made by these animals are simpler than human or mouse antibodies, an important feature conserved among all of these antibodies is: A. The presence of both heavy and light chain polypeptides B. Antigen-binding sites comprised of VH and VL sequences C. The presence of exactly three constant region domains D. The presence of two antigen-binding sites per antibody E. The presence of multiple disulfide bonds linking antibody light chains to heavy chains

D. The presence of two antigen-binding sites per antibody

Mannose binding lectins (MBL) and ficolins are the two classes of proteins that can initiate the lectin pathway of complement activation. These proteins areselective for activating complement on the surfaces of microbial pathogens rather than host cells because: A. Their higher-order oligomeric structure can be assembled only after the monomers first bind to pathogen membranes. B. They only recruit MASP (MBL-associated serine proteases) proteins when boundto pathogen surfaces and not when bound to host cells. C. They only undergo the conformational change needed to activate MASP proteinswhen bound to a pathogen and not when bound to a host cell. D. They only bind to carbohydrate side chains and oligosaccharide modifications found on pathogen surfaces but not on host cell membranes. E. The activated MASP proteins are rapidly inactivated by hydrolysis when present on the surface of a host cell.

D. They only bind to carbohydrate side chains and oligosaccharide modifications found on pathogen surfaces but not on host cell membranes.

When a mixture of different IgG antibody proteins are treated with the enzyme papain, each antibody is cleaved into three roughly equal size fragments. From each original antibody, two of the three fragments are identical to each other, and represent the 'arms' of the antibody 'Y'. These fragments are known as Fab fragments. The third fragment is known as the Fc region, because this fragment will crystallize when purified. The reason a mixture of Fc fragments will crystallize is because: A. It is the only part of the antibody protein that can easily be purified at the high concentrations needed for crystallization. B. It has no disulfide bonds holding the domains together, as disulfide bonds will inhibit crystallization. C. It is the only fragment of the antibody that still has disulfide bonds, so it remains intact during the crystallization process. D. The Fc fragments of IgG are much more water soluble than the Fab fragments. E. All Fc fragments generated from a mixture of IgG molecules have the identical amino acid sequence.

E. All Fc fragments generated from a mixture of IgG molecules have the identical amino acid sequence.

Pathogenic infections induce damage to the host by a variety of mechanisms. While many mechanisms are direct effects of the pathogen, some damaging mechanisms result from the immune response to the infection, as illustrated in Figure Q2.2. Examples of damage caused by the host immune response are: A. Endotoxin production/ endotoxin B. Cell-mediated immunity/ direct cytopathic effect C. Endotoxin/ immune complex D. Direct cytopathic effect/ endotoxin E. Cell-mediated immunity/ immune complexes

E. Cell-mediated immunity/ immune complexes

An infection in the skin, such as a pimple, often produces pus. The major component of pus is: A. Toxic oxygen molecules released by macrophages B. Toxic nitrogen molecules released by macrophages C. NETs released by neutrophils D. Dead epithelial cells killed by lysozyme E. Dead and dying neutrophils

E. Dead and dying neutrophils

The production of antimicrobial peptides is one of the most evolutionarily ancient mechanisms of defense for multicellular organisms, and most eukaryotic species make many different forms of these proteins. For instance, human Paneth cells in the gastrointestinal epithelium make 21 different defensins. The reason for this diversity of antimicrobial peptides is: A. Epithelial cells make different forms than those made by neutrophils. B. Neutrophils make many different defensins and store them as inactive proteins in their secretory granules. C. Most of them are produced only in response to infection. D. The production of different peptides is induced following a bacterial infection versus a fungal infection. E. Each one has distinct activities against Gram-negative bateria, Gram-positive bacteria, or fungi.

E. Each one has distinct activities against Gram-negative bateria, Gram-positive bacteria, or fungi.

A key feature of TLR signaling is the ability to induce inflammatory cytokine gene expression extremely rapidly following TLR stimulation. This is accomplished by signaling pathways using several mechanisms to activate transcription factors that are already present in the cell prior to TLR stimulation, but are kept in an inactive state. These signaling pathways use all of the following mechanisms EXCEPT: A. Induced ubiquitination leading to protein degradation B. Induced ubiquitination inducing protein-protein interactions C. Induced phosphorylation leading to nuclear translocation D. Induced phosphorylation leading to kinase activation E. Induced phosphorylation preventing protein degradation

E. Induced phosphorylation preventing protein degradation

When complement proteins are covalently deposited onto the surface of a bacterium, this can sometimes lead to direct lysis of the bacterium. However, more commonly, the deposition of complement proteins onto the bacterial surface does not directly harm the bacterium. Instead, these complement proteins aid in bacterial elimination by: A. Recruiting antibodies to the bacterial surface, leading the antibody-dependent neutralization B. Providing a mechanism for phagocytes to use their Fc receptors to recognize andingest the bacterium C. Cross-linking carbohydrate structures on the bacterial surface, thereby preventing the bacterium from replicating D. Stimulating B lymphocytes to produce more antibodies against the bacterium E. Providing a mechanism for phagocytes bearing complement receptors to recognize and ingest the bacterium

E. Providing a mechanism for phagocytes bearing complement receptors to recognize and ingest the bacterium

In healthy adults, neutrophils represent approximately half of their white blood cells. During a bacterial infection, this number rises to >80%. One factor contributing to this rise is: A. Recruitment of neutrophils from tissues into the blood B. Proliferation of neutrophils at the site of infection C. Proliferation of neutrophils in the blood D. Differentiation of blood monocytes into neutrophils E. Release of neutrophils into the blood from the bone marrow

E. Release of neutrophils into the blood from the bone marrow

The alternative pathway of complement activation has an important role in innate immunity, due to its ability to greatly amplify the amount of C3b deposited onto the pathogen surface. This amplification occurs because: A. The C3 convertase of the alternative pathway is much more active than those of the classical and lectin pathways. B. The C3 convertase of the alternative pathway works as a soluble enzyme in the plasma. C. The C3 convertase of the alternative pathway cannot be inactivated by complement regulatory factors in the host. D. The C3 convertase of the alternative pathway is more efficiently recruited to pathogen surfaces than the C3 convertases of the classical and lectin pathways. E. The C3 convertase of the alternative pathway contains C3b, and can generate more of itself.

E. The C3 convertase of the alternative pathway contains C3b, and can generate more of itself.

One strategy for vaccine development currently under investigation is the use of pathogen-derived T cell epitopes as a component of the vaccine. For viral pathogens, implementing this strategy involves scanning the predicted amino acid sequences of the viral proteins for likely peptide epitopes that would bind to MHC class I and MHC class II molecules. In addition to the complication of MHC sequence polymorphism in the human population, another complication of this strategy for peptide epitopes that would bind to MHC class II proteins is: A. The importance of viral proteins containing peptides that are cleaved into 8-10 aminoacid long fragments. B. The ability of viruses to mutate their proteins to avoid MHC anchor residue sequences. C. The fact that long peptides (>13 amino acids) are rapidly degraded in cells. D. The fact that MHC class II proteins are intrinsically stable, even in the absence of binding to a peptide. E. The absence of defined sequence motifs that predict peptide binding to MHC class II molecules.

E. The absence of defined sequence motifs that predict peptide binding to MHC class II molecules.

Women with urinary tract infections caused by E. coli are generally treated with a course of antibiotics. A common complication of the antibiotic treatment is the occurrence of a vaginal yeast infection caused by Candida albicans, an organism that is normally present in very low numbers in the human vaginal tract. This complication occurs because: A. The E. coli infection damages the reproductive epithelium, causing a breach in the tight junctions and allowing invasion by the Candida albicans. B. The E. coli infection induces adhesion molecule expression on the reproductive epithelium, allowing attachment of the yeast. C. The antibiotic treatment kills all strains of fungi present in the reproductive tract, except the Candida albicans. D. The E. coli infection causes gastrointestinal distress leading to diarrhea. E. The antibiotics kill many of the commensal organisms in the reproductive tract, allowing overgrowth of the fungus

E. The antibiotics kill many of the commensal organisms in the reproductive tract, allowing overgrowth of the fungus

True/False: All mammalian TLRs have been shown to directly bind to microbial products, leading to TLR signaling.

False

True/False: Chemokines are small chemoattractant molecules made by epithelial cells, tissue macrophages, and endothelial cells in response to infection or injury. They differ slightly in sequence and structure based on the cells that secrete them, but all of them act to recruit both monocytes and neutrophils from the blood.

False

True/False: Like innate sensors of infections (TLRs, NLRs, RLRs), antibodies frequently recognize nucleic acids of pathogenic organisms.

False

True/False: Mucosal surfaces and external epithelia are major routes of pathogenic infection. Mucosal surfaces are found in tissues such as the gastrointestinal tract, the reproductive tract and the mouth and respiratory tract. While the mouth and respiratory tract are routes of virus but not bacterial infections, the gastrointestinal tract is the route for bacterial but not virus infections.

False

True/False: Our immune system efficiently kills all categories of microbes that attempt to colonize our bodies.

False

True/False: The antibody protein has two functional domains, one for antigen binding and a second to confer specific effector functions. These two functional domains are encoded by the antibody light chain and antibody heavy chain polypeptides, respectively.

False