Immuno Test#2

Immuno Quiz #2 Chapter 5 5,8,9,12,14,15 1. Indicate whether each of the following statements is true or false. If you think the statement is false, explain why. a. Vk gene segments sometimes join to C(gama)gene segments: False, Vk gene segments and C1 are located on separate chromosomes and cannot be brought together during gene rearrangement. b. With the exception of a switch to IgD, immunoglobulin class switching is mediated by DNA rearrangements: True c. Separate exons encode the transmembrane portion of each membrane immunoglobulin: True d. Although each B cell carries two alleles encoding the immunoglobulin heavy and light chains, only one allele is expressed: True e. Primary transcripts are processed into functional mRNA by removal of introns, capping, and addition of a poly-A tail: True f. The primary transcripts is an RNA complement of the coding strand of the DNA and includes both introns and exons: True 2. Explain why a Vh segment cannot join directly with a JH segment in heavy-chain gene rearrangement. -VH and JH gene segments cannot join because both are flanked by recombination signal sequences (RSSs) containing a 23-bp (2-turn) spacer. (see figure 5-6b). According to the one-turn/two-turn joining rule, signal sequences having a two-turn spacer can join only with signal sequences having a one-turn (12-bp) spacer. 3. Considering only combinatorial joining of gene segments and association of light and heavy chains, how many different antibody molecules potentially could be generated from germ-line DNA containing 500 VL and 4JL gene segments and 300 VH, 15 DH, and 4JH gene segments? Light chains: 500 x VL 3 4 JL=2 3 103 Heavy chains: 300 VH x 3 15 DH x 34 JH= 1.83 x 104 Antibody molecules: (2x3 103 LCs) x 3(1.8 x 3 104 HCs)=3.6 x 3 107 4. For each incomplete statement below, select the phrase(s) that correctly completes the statement. More than one choice may be correct. Recombination of immunoglobulin gene segments serve to Promote Ig diversification Assemble a complete Ig coding sequence 0 Allow changes in coding information during B-cell maturation Increase the affinity of immunoglobulin for antibody All of the above. Somatic mutation of immunoglobulin genes accounts for 1. Allelic exclusion 2. Class switching from IgM to IgG 3. Affinity maturation 4. All of the above 5. None of the above The frequency of somatic mutation in Ig genes is greatest during 1. Differentiation of pre-B cells into mature B cells 2. Differentiation of pre-T cells into mature T cells 3. Generation of memory B cells 4. Antibody secretion by plasma cells 5. None of the above Kappa and lambda light-chain genes 1. Are located on the same chromosomes 2. Associate with only one type of heavy chain 3. Can be expressed by the same B cell 4. All of the above 5. None of the above Generation of combinatorial diversity among immunoglobulins involves 1. MRNA splicing 2. DNA rearrangement 3. Recombination signal sequences 4. One-turn/two-turn joining rule 5. Switch sides g. The mechanism that permits immunoglobulins to be synthesized in either a membrane-bound or secreted for is 1. allelic exclusion 2. codominant expression 3. class switching 4. the one-turn/two-turn joining rule 5. differential RNA processing 5,8,9,12,14,15 5. What mechanisms generate the three hypervariable regions (complementarity-determining regions) of immunoglobulin heavy and light chains? Why is the third hypervariable region (CDR3) more variable than the other two (CDR1 and CDR2)? -Somatic mutation contributes to the variability of all three complementarity-determining regions. Additional variability is generated in the CDR3 of both heavy and light chains by junctional flexibility, which occurs during heavy-chain D-J and V-DJ rearrangements and light-chain V-J rearrangements, by P-nucleotide addition at heavy-and light-chain variable-region joints, and by N-nucleotide addition at the heavy-chain D-J and V-DJ joints. See table 5-3 8. Indicate whether each of the class switches indicated below can occur (yes) or cannot occur (no). a. IgM to IgD –No b. IgM to IgA-Yes c. IgE to IgG-No d. IgA to IgG-No e. IgM to IgG-Yes 9. Describe one advantage and one disadvantage of N-nucleotide addition during the rearrangement of immunoglobulin heavy-chain gene segments. -Random addition of N-nucleotides at the D-J and V-DJ junctions contributes to the diversity within the CDR3 of heavy chains, but this process can result in a nonproductive rearrangement if the triplet reading frame is not preserved. 12. Match the terms below (a-h) to the descriptions that follow. Each description may be used once, more than once, or not at all; more than one description may apply to some terms. RAG-1 and RAG-2 (5) -Enzymes expressed in developing B cells Double-strand break repair (DSBR) enzymes (5,6,9) -Enzymes expressed in developing B cells -Enzymes expressed in mature B cells -Enzymes that are defective in SCID mice Coding joints (1) -Junctions between immunoglobulin gene segments formed during rearrangement RSSs (4) -Conserved DNA sequences, located adjacent to V, D, and J segments, that help direct gene rearrangement P-nucleotides (2, 8) -Source of diversity in antibody heavy chains -Product of endonuclease cleavage of hairpin intermediates in Ig-gene rearrangement N-nucleotides (2,11) -Source of diversity in antibody heavy chains -Nucleotides added by TdT enzyme Promoters (3,7) -DNA regulatory sequences -nucleotide sequences located close to each leader segment in immunoglobulin genes to which RNA polymerase binds Enhancers (3,10) --DNA regulatory sequences -Nucleotide sequences that greatly increase the rate of transcription of rearranged immunoglobulin genes compared with germ-lined DNA 14. A which level, DNA or RNA, are each of the following activities determined? a. Membrane vs. secreted antibody-RNA b. IgM vs IgD-RNA c. V-J joining-DNA d. IgA vs IgE-DNA e. V-D-J joining-DNA 15. The tendency to become allergic can be inherited, based on a genetic predisposition favoring the production of IgE antibodies. However, the antigen that an individual is allergic to (the allergen) is not inherited. Knowing how antibody specificity is produced, explain this apparent contradiction. -Antibody specificity is not inherited from one’s parents. It is determined at the DNA level by random arrangements of genome coding for the antigen-binding region of the antibody. Thus, the tendency to produce IgE may be inherited from a patient, but the specificity of the IgE molecules will be determined differently in each individual Chapter 6 1a,b,c,d,f,g,h; 2; 3; 6; 7; 8; 10; 12; 13; 14 1. Indicate whether each of the following statements is true or false. If you think a statement is false, explain why. a. Indirect immunofluorescence is a more sensitive than direct immunofluorescence: true b. Most antigens induce a polyclonal response: true c. A papain digest of anti-SRBC antibodies can agglutinate sheep red blood cells (SRBCs): False: papain digestion yields monovalent Fab fragments, which cannot crosslink antigens. d. A pepsin digest of anti-SRBC antibodies can agglutinate SRBCs. true f. For precipitation to occur, both antigen and antibody must be multivalent. true g. Analysis of a cell population by flow cytometry can simultaneously provide information on both the size distribution and antigen profile of cell populations containing several different cell types : True h. ELISA tests using chemiluminescence are most sensitive than chromogenic ones and precipitation tests are more sensitive than agglutination test. False: agglutination tests are more sensitive. 2. You have obtained a preparation of purified bovine serum albumin (BSA) from normal bovine serum. To determine whether any other serum proteins remain in this preparation of BSA, you decide to use immunoelectrophoresis. a. What antigen would you use to prepare the antiserum needed to detect impurities in the BSA preparation? -Whole bolvine serum b. Assuming that the BSA preparation is pure, draw the immunoelecectrophoretic pattern you would expect if the assay was performed with bovine serum in a well above a trough containing the anitserum you prepared in (a) and the BSA sample in a well below the trough as shown below: (see figure) 3. The labels from four bottles (A,B, C, and D) of haptencarrier conjugates were accidentally removed. However, it was known that each bottle contained either (1) hapten 1-carrier 1 (H1-C1), (2) hapten 1-carrier 2 (H1-C2), (3) hapten 2-carrier 1 (H2-C1), or (4) hapten 2-carrier 2 (H2-C2). Carrier 1 has a molecular weight of 60,000 daltons, and carrier 2 has a molecular weight of over 120,000 daltons. Assume you have an anti-H1 antibody and an anti-H-2 antibody and a molecular-weight marker that is 100,000 daltons. Use Western blots you would expect from 1,2,3, and 4. Your answer should also tell which antibody or combination of antibodies was used to obtain each blot. -Bottle A:H1-C1. Bottle B: H2-C2. Bottle C: H2-C1. Bottle D: H1-C2 6.For each antigen or antibody listed below, indicate an appropriate assay method and the necessary test reagents. Keep in mind the sensitivity of the assay and the expected concentration of each protein. a. IgG in serum: ELISA b. Insulin in serum: ELISA or RIA c. IgE in serum: ELISA d. Complement component C3 on glomerular basement membrane: immunofloresence e. Anti-A antibodies to blood-group antigen A in serum: Agglutination f. Horse mean contamination of hamburger: ELISA g. Syphilis spirochete is a smear from a chancre. :Agglutination 7. Which of the following does not participate in the formation of antigen-antibody complexes? a. Hydrophobic bonds b. Covalent bonds c. Electrostatic interactions d. Hydrogen bonds e. Van der Waals forces 8. Explain the difference between antibody affinity an antibody avidity. Which of these properties of antibody better reflects its ability to contribute to the humoral immune response to invading bacteria? -Affinity refers to the strength of the interaction between a single antigen-binding site in an antibody and the corresponding ligand. Avidity refers to the total effective strength of all the interactions between multiple antigen binding sites in an antibody and multiple identical epitopes in a complex antigen. Because bacteria often have multiple copies of a particular epitope on their surface, the avidity of an antibody is a better measure than its affinity of its ability to combat bacteria. 10. In preparing a demonstration for her immunology class, an instructor purified IgG antibodies to sheep red blood cells (SRBCs) and digested some of the antibodies into Fab, Fc, and F(ab)2 fragments. She placed each preparation in a separate tube, labeled the tubes with a water-soluble marker, and left them in an ice bucket. When the instructor returned for her class period, she discovered that the labels had smeared and were unreadable. Determined to salvage the demonstration, she relabeled the tubes 1,2,3, and 4 and proceeded. Based on the test results described below indicate which preparation was contained in each tube and explain how you identified the contents. a. The preparation in Tube 1 aggultinated SRBCs but did not lyse them in the presence of complement. -tube 1 contained F(ab9’)2 fragments. Because these fragments contain two antigen-bidnging sites, they can crosslink and eventually agglutinate SRBCs. Activation of complement by IgG requires the presence of the Fc fragment, which is missing from F(ab9’)2 b. The preparation in tube 2 did not agglutinate SRBCs or lyse them in the presence of complement. However, when this preparation was added to SRBCs before the addition of whole anti-SRBC, it prevented agglutination of the cells in the presence of complement. -Tube 2 contained Fab fragments. Univalent Fab fragments can bind to SRBCs and inhibit subsequent agglutination by whole anti-SRBC c. The preparation in tube 3 agglutinated SRBCs and also lysed the cells in the presence of complement. -Tube 3 contained intact antibody d. The preparation in tube 4 did not agglutinate or lyse SRBCs and did not inhibit agglutination of SRBCs by whole anti-SRBC antiserum -Tube 4 contained Fc fragments. These fragments lack antigen- binding sites and thus cannot mediate any antibody effector functions. 12.You have taken a job in a clinical lab over the summer to help pay off yours student loans. You order a kit designed to detect Hantavirus antibodies in patient sera using indirect ELISA, but when it arrives there are no instructions, just bottles labeled “reagen A,” “reagent B” and so forth. Several patients have been potentially exposed to Hantavirus and you need to use this kit to determine if the patients have actually been exposed. a. Which of the following would be included in the kit as reagents required to run this assay? 1. Positive control soluble antigen 2. primary antibody to Hanta virus 3. Substrate 4. Enzyme-labeled secondary antibody to primary 5. Enzyme-labeled secondary antibody to virus 6. Antigen-coated plates B. using the kit, you obtain results for 3 patient sera (P1-P3 in the table). What are the titer of the patient sera (give a titer for each of the 3 patients)? Which (if any) of these patients were exposed? -Patient 1:1000; patient 2:no titer; patient 3:10; Patients 1 and 3 were possibly exposed, since they have developed antibodies to Hantavirus. Patient 2 has no titer and was therefore not exposed 13. Any new strain of flu has been discovered that has the potential to infect large numbers of people due to its high rate of transmission. To assess the severity of a wide-spread infection, you test whether average citizens already express antibodies that could cross-react with the flu antigens. First you run solublized surface antigens from the flu strain in lanes of an SDS-Page gel. One lane is then stained with the non-specific stain Coomassie blue (left in the figure above). The remaining lanes are electrophoretically transferred to nitrocellulose and cut into strips so that each lane can be incubated with normal volunteer sera as a primary antibody for Western blotting. The results, would you expect a widespread health crisis from the new flu strain? -all the western blot strips show some reactivity, meaning that each person tested had antibodies that would bind to at lease one of the flu antigens. This would indicate that the new strain is antigenically similar to existing strains and would be unlikely to cause a drastic problem if the general population reacts similarly to the tested volunteers. 14. Your research advisor has just discovered a new receptor thought to be important in the development of Alzheimer’s disease. Other lab members have cloned the receptor and transfected the gene into a cell line for further study. Your task is to perform cell sorting on the transfected cells to screen out nonexpressers and select a population of high-level expressers. You have available a rabbit antibody to the receptor, a control mouse antibody that binds to untrasfected cells, fluorescein-conjugated goat anti-mouse antibodies, and rhodamine-conjugated donkey anti-rabbit antibodies. a. describe how you would set up the FACS experiment. -The cells need to be incubated with both primary antibodies, rinsed, and then incubated with the secondary labeled antibodies. The sample is then applied to the instrument so the fluorochrome will be excited by the laser and deflected accordingly. b. Draw a representative FACS histogram of the expected results with the x axis showing the level of phodamine. Include in your historgrame where you would set the gates for cell separation. -The upper-left quadrant would contain cells expressing high levels of receptor, and the lover-right quadrant would contain untransfected cells or cells expressing low levels of receptor. Chapter 7 1,2,3,4,5a, 5c, 7a, 7d, 8 1. Indicate whether each of the following statements is true or false. If you think a statement is false, explain why. a. A single molecule of bound IgM can activate the C1q component of the classical complement pathway-True b. C3a and C3b are fragments of C3-true c. The C4 and C2 complement components are present in the serum in functionally inactive proenzyme form.-True d. Nucleated cells tend to be more resistant to complement-mediated lysis than red blood cells.-True e. Enveloped viruses cannot be lysed by complement because their outer envelope is resistant to pore formation by the membrane-attack complex- False-enveloped viruses can be lysed by complement because their outer enveloped is derived from the plasma membrane of a hose cell f. C4-deficient individuals have difficulty eliminating immune complexes. - True 2. Explain why serum IgM cannot activate complement by itself. -Serum IgM is in a planar form in which the complement binding sites in the Fc region are not accessible. Only after binding to antigen does IgM assume a conformation in which the complement-binding sites are accessible. 3. Genetic deficiencies have been described in patients for all of the complement components except factor B. Particularly severe consequences result from a deficiency in C3. Describe the consequences of an absence of C3 for each of the following: a. Activation of the classical and alternate pathways -Activation of classical pathway would not be affected. Activation of the alternate pathway would not occur. The alternate pathway relies on spontaneous cleavage of C3. b. Clearance of immune complexes -Clearance of immune complexes would be diminished because cleavage fragment C3b would not be available to attach immune complexes to erythrocytes via CR1 for clearance in the liver and spleen c. Phagocytosis of infectious bacteria -Phagocytosis would be diminished due to lack of opsonin C3b binding to bacterial cell surfaces. d. Presentation of antigenic peptides from infectious bacteria. -Presentation of antigens would be diminished indirectly due to inefficient phagocytosis of bacteria by macrophages and other phagocytic antigen-presenting cells 4. Summarize the four major functions of the complement system. -lysis of bacteria enveloped viruses, and cells by formation of the membrane attack complex; opsonization of invading cells to enhance phagocytosis; targeting of coated cells by immune system cells bearing complement receptors, increasing the inflammatory response at the site of infection; targeting immune complexes for clearance by offering biding sites to complement receptors on phagocytes and red blood cells. 5. Complement activation can occur via the classical, alternative, or lectin pathway. A. How do the three pathways differ in the substances that can initiate activation? -the classical pathway is initiate by immune complexes involving IgG or IgM; the alternative pathway generally is initiated by bacterial cell wall components; and the lectin pathway is initiated by binding of mannose-binding lectin (MBL) to microbial cell wall carbohydrates C. How do the biological consequences of complement activation via these pathways differ? -Complement activation by any of the three pathways has the same biological consequences because components mediating all the biological effects of complement are generated in all three 7. Briefly explain the mechanism of action of the following complement regulatory proteins. Indicate which pathway(s) each protein regulates. a. C1 inhibitor (C1InH) d. Decay-accelerating factor (DAF) See table 7-2 8. For each complement components or reaction, select the most appropriate description listed. Each description may be used once, more than once, or not at all. a. C3b-(4) -mediates opsonization b. C1, C4, C2, and C3-(5) -are early components of classical pathway c. C9-6 -has perforin-like activity d. C3, factor B, and factor D-2 -are early components of alternative pathway e. C1q-7 -binds to Fc region of antibodies f. C4b2a3b-11 -has C5 convertase activity g. C5b, C6, C7, C8, and C9-3 -compose the membrane-attack complex h. C3->C3a+C3b-1 -Reaction that produces major amplification during activation i. C3a, C5a, and C5b67-8 -have chemotactic activity j. C3a, C4a, and C5a-10 -induce degranulation of mast cells (are anaphylatoxins) k. C4b2a-9 -Has C3 convertase activity l. C3b+B->C3bBb+Ba-12 -Reaction catalyzed by factor D Chapter 8 -1 b,d,e,5,6,12,13,15a Indicate whether each of the following statements is true or false. If you think a statement is false, explain why. b. Antigen-presenting cells express both class 1 and class 2 MHC molecules on their membranes -True d. In outbred populations, an individual is more likely to be histocompatible with one of its parents than with is siblings -false: the offspring of heterozygous parents inherit one MHC haplotype from each parent and thus will express some molecules that differ from those of each parent, for this reason, parents and offspring are histoincompatible. In contrast, siblings have a one in four chance of being histocompatible e. Class 2 MHC molecules typically bind to longer peptides than do class 1 molecules -True 5. Draw diagrams illustrating the general structure, including the domains, of class 1 MHC molecules, class 2 MHC molecules and membrane-bound antibody on B cells. Label each chain and the domains within it, the antigen-binding regions and regions that have the immunoglobulin-fold structure. -see figure 8-3,4-6, and 4-25 6. One of the characteristic features of the MHC is the large number of different alleles at each location. a. Where are most of the polymorphic amino acid residues located in MHC molecules? What is the significance of this location? -The polymorphic residues are clustered in short stretches primarily within the membrane-distal domains of the class 1 and class 2 MHC molecules. These regions form the peptide-binding cleft of MHC molecules b. How is MHC polymorphism thought to be generated? -Thought to arise by gene conversion of short, nearby homologous DNA sequences within unexpressed pseudogenes in the MHC to functional class 1 or class 2 genes. 12. Define the following terms: a. Self-MHC restriction: Self-MHC restriction is the attribute of T cells that limits their response to antigen associated with self-MHC molecules on the membrane of antigen-presenting cells or target cells. In general, CD4+ TH cells are class 2 MHC restricted, and CD8+ TC cells are class 1 MHC restricted, although a few exceptions to this pattern occur. b. Antigen processing-Antigen processing involves the intracellular degradation of protein antigens into peptides that associate with class 1 or class 2 MHC molecules. c. Endogenous antigen-endogenous antigens are synthesized within altered self cells (e.g. virus-infected cells or tumor cells), are processed in the cytosolic pathway and are presented by class 1 MHC molecules to CD8+ TC cells d. Exogenous antigen-are internalized by antigen-presenting cells, processed in the endocytic pathway and presented by class 2 MHC molecules to CD4+TH cells. 13. For each of the following cell components or processes, indicate whether it is involved in the processing and presentation of exogenous antigens (EX), endogenous antigens (EN) or both (B). Briefly explain the function of each Item. a. Class 1 MHC molecules: EN-class 1 molecules associated with antigenic peptides and display them on the surface of target cells to CD8+ Tc cells b. Class 2 MHC molecules: Ex: class 2 molefules associate with antigenic peptides and display them on the surface of APCs to CD4+ TH cells. c. Invariant (li) chains-: EX: The invariant chain interacts with the peptide- binding cleft of class 2 MHC molecules in the rough endoplasmic reticulum, thereby preventing binding of peptides from endogenous antigens. IT also assists in folding of the class 2 alpha and beta chains and in movement of class 2 molecules from the RER to endocytic compartments. d. Lysosomal bydolases: EX e. TAP1 and TAP2 proteins: EN f. Transport of vesicles from the RER to the golgi complex: B g. Proteasomes: EN h. Phagocytosis or endocytosis: EX i. Calnexin:EN j. CLIP: EX k. Tapasin :EN 15a. Cells that can present antigen to TH cells have been classified into 2 groups-professional and nonprofessional APCs. Name the 3 types of professional APCs. For each type, indicate whether it expresses class 2 MHC molecules and a costimulatory signal constitutively or must be activated before doing so. -dendritic cells constitutively express both class 2 MHC molecules and costimulatory signal B cells: constitutively express class 2 molecules but must be activated before expressing the B7 costimulatory signal. Macrophages: must be activated before expressing either class 2 molecules or the B7 costimulatory signal. Chapter 9: 1a-h, 3,4,5,9 1. Indicate whether each of the following statements is true or false. If you think it is false, explain why. a. Monoclonal antibody specific for CD4 will coprecipitate the T-cell receptor along with CD4. -False: the distance between CD4 and the TCR is too great for them ro coprecipitate; however, CD3 and the TCR are close enough that they will coprecipitate in response to monoclonal anti-CD3 Subtractive hybridization can be used to enrich for mRNA that is present in one cell type but absent in another cell type within the same species. -True c. Clonotypic monoclonal antibody was used to isolate the T-cell receptor. -True d. The T cell uses the same set of V, D, and J gene segments as the B cell but uses different C gene segments. -false: the TCR variable-region genes are located on different chromosomes from the Ig variable-region genes e. The alpha Beta TCR is bivalent and has two antigen-binding sites. -false: all T-cell receptors have a single binding site for peptide-MHC complexes f. Each alpha beta T cell expresses only one beta-chain and one alpha- chain allele. -false: because allelic exclusion is not complete for the TCR alpha chain, a T cell occasionally expresses two alpha chains resulting from rearrangement of both alpha-chain alleles g. Mechanisms for generation of diversity of T-cell receptors are identical to those used by immunoglobulins. -false: the generate diversity by somatic mutation as immunoglobulins do h. The Ig-Alpha/Ig=beta heterodimer and CD3 serve analogous functions in the B-cell receptor and T-cell receptor, respectively. -True 3. Draw the basic structure of the alpha beta T-cell receptor and comare it with the basic structure of membrane-bound immunoglobulin. (see figure 9.3) 4. Several membrane molecules, in addition to the T-cell receptor, are involved in antigen recognition and T-cell activation. Describe the properties and distinct functions of the following T-cell membrane molecules: a. CD3- a complex of 3 dimers containing 5 different polypeptide chains. It is required for the expression of the T-cell receptor and plays a role in signal transduction across the membrane. CD3 and the T-cell receptor associate to form the TCR-CD3 membrane complex. (see figure 9.9) b. CD4 and CD8- CD4 and CD8 interact with the membrane-proximal domains of class 2 and class 1 MHC molecules, respectively, thereby increasing the avidity of the interaction between T cells and peptide- MHC complexes. CD4 and CD8 also play a role in signal transduction c. CD2- CD2 and other accessory molecules (LFA-1, CD28, and CD45R) bind to their ligands on antigen-presenting cells or target cells. The initial contact between a T cell and antigen-presenting cell or target cell probably is mediated by these cell adhesion molecules. Subsequently, the T-cell receptor interacts with peptide-MHC complexes. These molecules also may function in signal transduction. 5. Indicate whether each of the properties listed below applies to the T-cell receptor (TCR), B-cell immunoglobulin (Ig), or both (TCR/Ig). a. Is associated with CD3-TCR b. Is monovalent -TCR c. Exists in membrane-bound and secreted forms -Ig d. Contains domains with the immunoglobulin-fold structure-TCR/Ig e. Is MHC restricted -TCR f. Exhibits diversity generated by imprecise joining of gene segments- -TCR/Ig g. Exhibits diversity generated by somatic mutation-Ig 9. The gamma lambda T-cell receptor differs from the alpha beta T-cell receptor in both structural and functional parameters. Describe how they are similar to each other and different from the B-cell antigen receptors. -Although Alpha beta and gamma lambda T-cell receptors have some structural differences (figure 9-2) and functional differences in the type of antigen that is recognized, they have in common the fact that both are cell surface molecules. Immunoglobulins may be surface receptors on B cells, but their major function is to serve as soluble mediators of immunity. There is no evidence for activity of soluble forms of either the alpha beta or gamma lambda T-cell receptors. Chapter 10: 7, c, d, e, f, g, h, k; 11-13 7. Fill in the blank(s) in each statement below with the most appropriate term(s) from the box below. Terms may be used once, more than once, or not at all. c. Dendritic cells express _____ constitutively, whereas b cells must be activated before they express this membrane molecule: B7 Activation of TH cells results in secretion of ___ and expression of its receptor, leading to proliferation and differentiation. IL-2 The costimulatory signal needed for complete T-cell activation is triggered by interaction of ______ on the T cell and ____ on the APC. -CD28; B7 Knockout mice lacking class I MHC molecules fail to produce thymocytes bearing _______. –CD8 Macrophages must be activated before they express _____ molecules and _______molecules. –Class II MHC; B7 T cells bearing _____ are absent from the lymph nodes of knockout mice lacking class II MHC molecules. –CD4 k. _____ stimulates and ______inhibits T-cell activation when engaged by _____ or on antigen-presenting cells. –CD28 stimulates and CTLA4 inhibits 11. Several basic themes of signal transduction were identified and discussed in this chapter. What are these themes? Consider the signal transduction process of T-cell activation and provide an example for each of the five themes discussed. -Signal transduction begins with the interaction between a signal and its receptor. The interaction between the TCR and a T-cell antigen such as an MHC-peptide complex. Many signal transduction pathways involve the signal induced assembly of some components of the pathway; these assemblies utilize adaptor proteins LAT and SLP-76 in TCR signaling. Signal reception often leads to the generation within the cell of a “second messenger,” a molecule or ion that can diffuse to other sites in the cell and evoke metabolic changes. DAG and IP3 function as second messengers in TCR signaling. Protein kinases and protein phosphates are activated or inhibited. ZAP-70 and p46LcK function as protein kinases in the first steps of the pathway. Calcineurin functions as a phosphatase, removing a phosphate from NFAT and allowing it to translocate into the nucleaus, where it acts with NF-kbeta as a transcriptional activator. Signals are ampligied by enzyme cascades. Several enzyme cascades function in TCR signaling. These include the PKC (protein kinase C) and RAS/Map kinase pathway. 12. Whereas the majority of T cell in our bodies express an alpha beta TCR, up to 5% of T cells express the gamma lambda TCR instead. Explain the difference in antigen recognition between these 2 cell types. -Gamma Delta T cells do not have a requirement that antigen be presented by MHC. Thus, they are not limited to recognition of protein antigens. The recognition process seems to be closer to that pattern recognition receptors found on innate immune system cells. 13. T cells can be found that do not become stimulated when presented with their cognate antigen, whereas other T cells can be found that act as effector cells without having been presented with their cognate antigen. Explain how such T-cell activation/lack of activation can occur. Compare the signaling events that lead to these responses in your answer. -Encountering antigen can make T cells anergic if they receive a signal through the TCR (signa 1) but no signal from CD28 (signal 2). In contrast, if Tcells are bound by superantigens, the TCR will be engaged regardless of antigen specificity. The interaction is tight enough to allow both signals to occur, and polyclonal activation is seen. Chapter 11. 1a,b,d,e,f,g; 3; 6b,e,g; 7; 8; 10a,b,c,d; 11a,b; 13a,c,d,e,f,g; 14b,d. Indicate whether each of the following statements concerning B-cell maturation is true or false. If your think a statement is false, explain why. Heavy Chain VH-DH-JH rearrangement begins in the pre-B-cell stage. False: the Vh-DH-JH rearrangement occurs during the pro-B cell stage; successful completion of heavy-chain rearrangement marks the beginning of the pre-B cell stage, in which membrane bound u chains are expressed. Immature B cells express membrane IgM and IgD. -False- immature B cells express only IgM d. The surrogate light chain is expressed by pre-B cells. -True e. Self-reactive B cells can be rescued from negative selection by the expression of a different light chain. -True f. In order to develop into immature B cells, pre-B cells must interact directly with bone marrow stromal cells. -False: Pro-B cells must interact with stromal cells to develop into pre-B cells. Progression of pre-B cells into immature B cells requires IL-7 released from stromal cells but no direct contact. g. Most of the B cells generated every day never leave the bone marrow as mature B cells. –true 3. Describe the general structure and probable function of the B-cell-coreceptor complex. -The B-cell coreceptor consists of 3 membrane proteins: TAPA-1, CR2, CD19, the latter belong to the Ig superfamily. The CR2 component can bind to complement-coated antigen bound to the B-cell receptor (BCR). This binding results in the phosphorylation of phosphorylated CD!( and can trigger signal transduction pathways that begin with phospholipase C. 6. Fill in the blanks in each statement with the most appropriate terms from the following list. Terms may be used more than once or not at all. b. Initial activation of naïve B cells induced by thymus dependent antigens occurs within the ______ of the lymph nodes. Paracortex e. Class switching occurs in the ______ and requires direct contact between B cells and _____. Light zone; TH cells Within lymph nodes, plasma cells are found primarily in the ____ of secondary follicles. Medulla 7. Activation and differentiation of B cells in response to thymus dependent (TD) antigens requires TH cells, whereas the B-cell response to thymus-independent (TI) antigens does not. a. Discuss the difference in the structure of TD, TI-1, and TI-2 antigens and the characteristics of the humoral responses induced by them -See table 11-2 b. Binding of which classes of antigen to mIg provides an effective competence signal for B-cell activation -TI antigens 8. B-cell activating signals must be transduced to the cell interior to influence developmental processes. Yet the cytoplasmic tails of all isotypes of mIg on B cells are too short to function in signal transduction. How do naïve B cells transduce the signal induced by cross-linkage of mIg by antigen? -Each mIg molecule is associated with one molecule of a heterodimer called Ig-alpha/Ig Beta, forming the B-cell receptor (BCR). Both Ig-alpha and Ig-beta have long cytoplasmic tails, which are capable of mediating signal transduction to the cell interior. (see figure 11-8) b. Describe the general result of signal transduction in B cell during antigen-induced activation and differentiation -B-cell activating and differentiating signals- provided by antigen binding, interaction with TH cells, or cytokine binding-trigger intracellular signal transduction pathways that ultimately generate active transcription factors. These then translocate to the nucleus, where they stimulate or inhibit transcription of specific genes 10. Indicate whether each of the following statements is true or false. If you believe a statement is false, explain why. a. Cytokines can determine which branch of the immune system is activated. -True b. Immunization with a hapten-carrier conjugate results in production of antibodies to both hapten and carrier epitopes. –True c. All the antibodies secreted by a single plasma cell have the same idiotype and isotype. –true d. If mice are immunized with HRBCs and then are immunized a day later with SRBCs, the antibody response to the SRBCs will be much higher than that achieved in control mice immunized with SRBCs. -–False: antigenic competition will reduce the response to SRBC 13. True or False? a. CD21 is not only a complement receptor, it is an essential part of the B-cell receptor complex -True b. Signal transduction through the BCR complex results in transport of AP-1 to the cytosol. –False: Ap-1 is a transcription cascade will translocate to the nucleus from the cytosol c. Booster shots are required because repeated exposure to an antigen builds a stronger immune response. -True d. IgA is made against TI antigens -False: class switching is a feature of the response to thymus dependent antigens, arising from interactions with TH cells. Thymus Independent antigens can activate B cells without the assistance from T helper cells, including the interactions that lead to class switching. e. B Cells mature into effector cells in the thymus. -False: B cells mature into effector cells in the lymph node f. After a plasma cell secretes large amounts of antibody and little free antigen is present, the cell stops secreting antibody because its BCR is no longer stimulated. -False: As B cells develop into plasma cells, production of membrane immunoglobulin ceases in favor of secreted antibody, rendering plasma cells unresponsive to the presence of antigen. g. TI-1 antigens are substances such as LPS that can activate B cells nonspecifically at high concentrations. -True 14. Fill in the Blanks b. The cytokine _____________ induces B cells to undergo class switching to IgE. -IL-4 d. Mature _________ produce large amounts of soluble IgG. -Plasma cells **B cell maturation slide: might see drawing of it! And know what each part is and does -lymphokind receptor -cup on cell-about to be further activated lymphokind