Immunology Exam 3 - Questions and Answers Patients with the disease X-linked lymphoproliferative syndrome (XLP) lack expression of the small adapter
... [Show More] protein SAP, which associates with receptors of the SLAM family. One characteristic of this disease is an inability of cytotoxic T cells to control infections with a virus, Epstein-Barr virus (EBV), that replicates in B cells. This defect in control of EBV results from: A. A defect in antibody responses to EBV due to impaired T cell help for B cells B. A defect in adhesion of cytotoxic T cells to EBV-infected B cells C. Impaired migration of activated B cells to the germinal center D. Impaired survival of activated B cells, normally induced by CD40 stimulation E. A defect in TFH differentiation, normally induced by ICOS on B cells binding to ICOS-ligand on TFH cells True/False: Once B cells begin secreting antibodies, they cease dividing and have a life-span of only a few days False The germinal center is a region within the secondary B cell follicle where sustained B cell proliferation and differentiation take place. The processes of B cell proliferation and differentiation, including affinity maturation and class switching, require periodic interactions of the germinal center B cells with CD4 TFH cells. These periodic interactions between the B cells and TFH cells can occur: A. When B cells cycle between the dark zone and the light zone of the germinal center B. When B cells leave the germinal center and migrate through the T-cell zone on their way to the blood C. When B cells migrate and form a primary focus of antibody-secreting plasmablasts in the medullary cords of the lymph node D. When B cells migrate to the border between the T-cell zone and the B-cell zone of the lymph node E. When B cells up-regulate CXCR4 and migrate into the dark zone of the germinal center In germinal centers, proliferating B cells undergo a process called somatic hypermutation, in which mutations are introduced into the V regions of the antibody heavy and light chain genes. When this process is complete after several weeks, the overall affinities of the antibodies produced are greatly increased compared to those present early in the primary response. The somatic hypermutation process leads to increased antibody affinity because: A. Mutations that decrease the antibody affinity lead to an arrest of B cell proliferation. B. B cells making higher affinity antibodies receive more help from TFH cells. C. Somatic hypermutations only take place in the sequences encoding the CDR1, CDR2, and CDR3 regions. D. Mutations that increase antibody affinity lead to an increased rate of B cell proliferation E. The majority of nucleotide changes introduced by AID don't change the amino acid coding sequence Studies show that about 50-100 different B cells initially seed each germinal center (d7 post-infection). These different B cells are represented by different colored circles in a white oval (germinal center) in Figure Q10.9. Which of the choices shown best represents the B cell population that would be found in the same germinal center approximately two weeks later? D (all teal) The process of somatic hypermutation of antibody V regions sequences is initiated by the enzyme AID. This enzyme targets cytidine residues in the DNA sequence that are normally part of a G:C pair in the double-stranded DNA. Yet the hypermutation process generates mutations at both G:C and A:T base pairs of the original sequence because: A. Following AID action, a double-stranded DNA break plus chewing back of the ends occurs before re-ligation of the sequence. B. The error-prone polymerase repairs the sequence by inserting random nucleotides. C. There are two different pathways of repair target, one targeting G:C and one targeting A:T base pairs. D. B cells are the only cells to express the enzyme uracil-DNA glycoslyase (UNG). E. During active transcription both A:T and G:C base pairs are temporarily single-stranded Unlike somatic hypermutation, class switching occurs in discrete sequence regions upstream of the immunoglobulin heavy chain coding sequences (called switch regions). One key element in directing the enzyme AID to a specific switch region is the opening of the DNA duplex combined with polymerase stalling during active transcription in that region. A second key feature of directing AID to a specific switch region is: A. The processed RNA from the switch region guides AID to this site in the DNA B. The binding of DNA-PK's to the switch region sequence in the DNA C. The presence of double-stranded breaks in the DNA in this region D. The binding of AID to the RNA polymerase that is transcribing the switch region E. The predominance of G:C base pairs in the switch sequence In cell culture experiments, purified B cells expressing IgM can be induced to switch to producing IgE by stimulating them with an antibody to CD40 (a stimulatory antibody) plus the cytokine IL-4. In an individual undergoing an immune response, these signals would normally be provided by: A. Germinal center stromal cells B. Other B cells in the germinal center C. Follicular dendritic cells in the germinal center D. Any CD4 T cell in the same lymph node E.TFH cells in the germinal center [Show Less]