03-390 Immunology Exam I - 2014 Name:_____________________
03-390 Immunology Exam I - 2014 Name:_____________________ Instructions: This exam consists of 80 points. You should allot ~1 min/point. On questions with choices, all of your attempts will be graded and you will receive the highest grade. You may answer any question with a diagram, just be sure that it is adequately labeled. Use the space provided, or the back of the preceding page. 1. (4 pts) Compare and contrast one property of the innate system to the acquired system. For the property you selected, is the innate system “better” (or “worse”) than the acquired system in the elimination of pathogens. Briefly justify your answer. Speed – innate is faster and therefore better because it can deal with pathogens immediately. Ever present – innate is always there, this is better because can deal with pathogens immediately Memory – innate has no memory – this is worse because the response is the same. In the acquired system the presence of memory allows a faster and more effective response. Specificity – the innate system is less specific than the adaptive, which is worse – it is better to have a specific response. Adaptability – the innate system is not adaptable, which means it cannot become more effective at fighting the pathogen. 2. (4 pts) Please do one of the following choices. Choice A: Many brands of yogurt contain active (living) bacteria. How might these bacteria provide protection against pathogens? Choice B: Explain why mucosal membranes are protected by both physical and physiological barriers. Choice C: Explain why the skin provides protection by both physical and physiological barriers. Choice A: they establish a protective biofilm that will prevent pathogens from getting to the host. Choice B: Mucus traps organisms (physical) and ciliated cells remove the mucus (physiological) Choice C: Dead skin cells are a physical barrier. Fatty acids, low pH, and antibacterial peptides are a physiological barrier. 3. (5 pts) Briefly discuss the common features of the mechanism by which neutrophils, macrophages, and dendritic cells kill pathogens. Page1 Pathogen is taken up by phagocytosis or receptor mediated endocytosis Phagosome fuses with 1’ granuale, bringing in digestive enzymes Phagosome fuses with 2’ granuale, bringing in oxidative enzymes, generating reactive species Phagosome fuses with lysosome, drop in pH activates digestive enzymes. Pathogen is dead (hopefully) at this point. 03-390 Immunology Exam I - 2014 Name:_____________________ 4. (5 pts) Select any one complement pathway and briefly describe how that particular pathway is activated. Alternative: Activation is by the spontaneous hydrolysis of C3 to iC3b, thio-ester hydrolysis. Binds to factor B, which is cleaved to Bb by factor D. This is a soluble C3 convertase, it makes fixed (membrane attached) C3b, which then becomes the C3 convertase, using the same as above (B to Bb). Lectin Pathway: Mannose binding lectin binds to mannose on the surface of pathogens. Activates MASP-1, which cleaves itself and MASP-2 Activated MASP-2 cleaves C2 and C4 to produce C2aC4b – C3 convertase. Alternative Pathway: Antibody binds to antigen on surface, or C-reactive protein binds to phosphatidyl Choline (PC) lipids. C1q binds to antibody or C-reactive protein. Activates C1r, which cleaves itself and C1s Activated C1s cleaves C2 and C4 to produce C2aC4b – C3 convertase. 5. (5 pts) Please do one of the following choices. Choice A: Why are deficiencies in C4 less severe than deficiencies in C3? Choice B: How would a deficiency in any of the following: DAF, MCP, factor I, factor H, affect the well-being of an individual? Choice C: In what way(s) does the complement pathway lead to/cause the elimination of pathogens? Choice A: C4 is only required for the lectin and classical pathway, it is not a component of the alternative. Therefore the alternative pathway can still function. Choice B: These are all factors that reduce the amount of C3 convertase. The absence of these factors would mean that C3 convertase could accumulate on the host-cells, causing opsinization and lysis. Choice C: Three ways: i) opsinization by C3b – enhancing receptor mediated endocytosis. ii) Production of C3a and C5a – enhance inflammation. Iii)Formation of the membrane attack complex (MAC) that causes cell contents to leak out. Page2 6. (6 pts) Select any one of the following molecules: a) TNFα, b) histamine, c) IL-1, d) IL-8, e) bradykinin, and answer both of the following questions. i) State how it is released during the inflammatory response (i.e. what triggers the release). ii) Describe its major role in the inflammatory response and how this role aids in the elimination of pathogens. TNFa – Increases permeability of endothelium, allowing cells, protein, and fluid into the tissue. Additional cells (neutrophils) will kill pathogens, complement proteins will enhance complement. IL-1 - produced by activated macrophages due to TLR4 activation. Causes endothelium to produce IL-8, which binds to neutrophils and increases the affinity of their adhesion molecules – increasing the recruitment of neutrophils to the site. IL-8 - produced by activated macrophages due to TLR4 activation. Acts as a chemotactic agent to bring neutrophils to the site of infection. Bradykinin – produced by tissue damage. Causes an increase in diameter of the blood vessel. This slows down the flow to make it easier for neutrophils to enter. 03-390 Immunology Exam I - 2014 Name:_____________________ Page3 7. (6 pts) Select either an acute inflammatory or a systemic inflammatory response and: i) Give the name of the cytokine that is most closely associated with that process (1 pt). ii) What is the role of that cytokine in the response (5 pts). Acute – IL6 acts in an endocrine fashion causing: i) fever by interaction with the hypothalamus, ii) protein synthesis in the liver – producing C-reactive protein that will enhance complement, and other complement factors. Systemic – TNFα – released by macrophages in the liver and spleen due to pathogens in the blood. It causes an increase in vascular permeability, causing rapid loss of blood volume, leading to organ failure and death. 8. (6 pts) Please do one of the following choices: Choice A: What induces an anti-viral response, and how does the response protect cells from viruses? Choice B: How do NK cells decide whether to kill virally infected cells? Choice C: Briefly discuss why cell death through apoptosis is beneficial, from an immunological perspective? Choice D: Compare and contrast the activation and killing of virally infected cells by NK and T CTL cells. Choice A: Detection of dsRNA by TLR3 causes cells to release INF-α and INF-β. The dsRNA originates from a dsRNA virus. The antiviral response by uninfected cells, in reaction to these cytokines, is to shut down protein synthesis and induce the production of a dsRNase. Choice B: They detect reduced levels of MHC, or the presence of activation (“+”) signals on the surface of the infected cell. Choice C: Apoptosis keeps the cell contents within membrane vesicles, thus antigens that were inside the cell and normally hidden from the immune system will remain that way. It also prevents the spread of viruses from the infected cell. Choice D: NK cells are activated by “+” signals or low MHC. TCTL are activated by detection of a foreign peptide on class I MHC. Both cells kill by perforin/granzymes (induced apoptosis) or FasL/Fas trimerization (which also induces apoptosis). 9. (8 pts) Please do one of the following choices: Choice A: Outline the major steps that occur in the development of a B-cell from a stem cell to a naïve B-cell. Your answer should focus on important check-points in the developmental process. In bone marrow: HC rearrangement, checkpoint for functional HC using surrogate light chains. LC rearrangement, checkpoint for functional LC 1st check for self-tolerance, self-reactive B-cells killed. In lymph node: 2n check for self-tolerance Naïve B-cell leaves the lymph node. Choice B: Outline the major steps that occur in the development of plasma cells from naïve B-cells. Your answer should focus on key cell-surface molecules and the interaction between these molecules. Naïve B cells captures antigen with its B –cell receptor – specific interaction Peptide from antigen presented on class II MHC Peptide-MHCII complex recognized by TCR on TH cells – specific interaction. Activation of B-cell B-cell undergoes class switching and affinity maturation. Choice C: Outline the major steps that occur in the development of cytotoxic T-lymphocytes (TCTL) from naïve TC cells. Your answer should focus on key cell-surface molecules and the interaction between these molecules. TC recognizes foreign peptide presented on class I MHC – specific interaction. Activation of TC cell requires : i) co-stimulation via b7 on activated dendritic cell or ii) the presence of IL-2 secreted by a near-by TH cell 03-390 Immunology Exam I - 2014 Name:_____________________ 10. (5 pts) Secondary lymphatic tissues, such as lymph nodes, spleen, and MALT tissue all have one property or characteristic in common. What is that characteristic and why is it important in the generation of acquired immunity? They all have a high concentration of B- and T-cells. Since the reaction between MHC the TCR is specific, and a rare event, the high concentration helps ensure an APC will be able to find a T-helper cell to activate it. 11. (8 pts) Select any one of the following antibodies (IgM, IgG, IgE, IgA) and describe/draw its structure and provide one example of a specialized role for the antibody in the elimination of pathogens. The monomeric form of the Ab should contain two light chains, two heavy chains, and some indication of where the antigen bonds. IgM – pentameric – good for agglutination of antigens due to its large size. Also effective at activating complement because it has two Fc regions close together. IgA – dimer – secreted by MALT tissue to go outside the body and binding to pathogens before they can enter. IgG – monomer – good for physical blocking of pathogen because it can achieve a high density because it is small. IgE – monomer – binds to Fc receptor on mast cells. Binding of antigen to IgE causes degranulation of mast cells, helping eliminate parasites. Page4 12. (10 pts) Briefly describe how the exons for the VH and VL domains of antibodies are formed. Your answer should focus on the features of this process that lead to diversity of the heavy and light chains. The DNA encoding the variable exons of the HC and LC consist of a number of different segments. The HC is made by joining one V segment to one D and one J segment. The light chain is made by joining one V to one J. This is catalyzed by Rag1/Rag2 enzymes recognizing the 1+2 or 2+1 rule for recombination signal sequences. Diversity is generated by combinations, i.e. the number of heavy chains is nV x nD x nJ. Diversity is also generated during the joining process by: -imprecise joining (unequal crossover) -generation of P-nucleotides when hairpin is broken open -addition of random N-nucleotides to heavy chain V-D and D-J joints. 03-390 Immunology Exam I - 2014 Name:_____________________ 13. (2 pts) What additional property, besides how the exons are made, of the heavy and light chains has a significant contribution to diversity? Hint - this property is related to structural features of the two chains. The affinity of the CL domain to the CH1 domain is high, allowing any light chain to pair with any heavy chain, so the total diversity is the number of HC x number of LC. 14. (6 pts) Please do one of the following choices: Choice A: Briefly describe allelic exclusion and its importance to the normal function of B-cells. After the gene for one chain is successfully rearranged, the rearrangement of the remaining allele is suppressed, so only on allele is expressed. This ensures that there is a homogeneous BCR on the B-cells Thus a plasma cell will only produce a single antibody, which will be effective against the pathogen. If the B-cell had more than one type of BCR, the plasma cell would produce a number of different Ab, only one of which would be useful. Having a homogeneous BCR reduces the likelihood a B-cell will be self-reactive. Choice B: Describe the role of mRNA processing in the co-expression of IgM and IgD. The exons for the constant regions of IgM and IgD are adjacent to each other, just downstream (3’) to the variable exon. There are polyA addition sites at the end of the constant exons for the IgM and the IgD constant exons. If the first polyA site is used, then only the IgM coding region is left in the mRNA (the IgD coding region would be removed during the addition of the polyA). If the second polyA site is used, then the transcript contains both the IgM and the IgD exons. The IgM exons are spliced out and an IgD antibody is produced. Choice C: Describe the role of mRNA processing in the production of soluble versus membrane bound antibody. Page5 At the 3’ end of the constant exons for each type of heavy chain there are three exons: S- M1 – M2. There are polyA addition sites after S and M2. If the first polyA site is used, the M1 and M2 exons are removed and the transcript only contains the S (soluble) exon. Thus the antibody will be soluble. If the second polyA site is used, the transcript will contain all three exons, the S-exon is removed by alternative splicing, leaving the M1 and M2 exons. These code for hydrophobic amino acids, anchoring the heavy chain in the membrane. Bonus Questions (1 pt each) (use back of previous page). 1. Skin grafts between cheetahs are usually accepted. Why? Cheetahs are highly inbred, therefore they have common MHC alleles, thus the transplanted tissue would appear to be “self” due to the fact that it would have the same MHC alleles. 2. How does breastfeeding benefit the immune system of the new-born? IgA is present in the milk, providing immunity for the baby. 3. Why is cancer a transmissible disease for a certain type of cancer that affects Tasmanian devils? The cancer cells that are transmitted have no MHC, thus they are ignored by the immune system of the affected individual.