1. Isotype switching driven by extrafollicular helper T cells is observed promin
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Question
1. Isotype switching driven by extrafollicular helper T cells is observed prominently in: a. Mucosal epithelium b. Germinal centers Mantle zones Red pulp of the spleen c. d. 2. The enzyme known as activation-induced cytidine deaminase (AID) is critical for a. b. c. d. Positioning gene segments next to one another prior to recombination events Repairing double-stranded breaks in DNA Successful isotype (class) switching and somatic hypermutation events Uracyl N-glycosylase (UNG) 3. The somatic hypermutations that occur in T cell-dependent B cell activation result in low-affinity BCRs. of the a. N-nucleotide region addition b. ADP-ribosylation c. Receptor editing d. Affinity maturation 4. Which of the following is a prominent characteristic of extrafollicular B cell activation? a. Early isotype (class) switching and short-lived plasma cells b. Early somatic hypermutation and generation of long lived memory B cells c. Further interactions with extrafollicular dendritic cells d. Migration of B cells to the mantle zone and heightened proliferation CD4 T cell subsets described in class, follicular helper T cells (Ta) produce a signature cytokine. Indicate which of the following, from the list below, is considered the Taw signature cytokine a. IL21 b. IL12 c. IFNy d. 1L4 e. TGF-beta 1 6. Enhanced B cell activation may result after: a. A long period of B cell anergy b. The first round of somatic hypermutation c. B-1 B and MZ B cells internalize lipid antigens Complement-coated antigen simultaneously ligate the BCR and complement receptor 2 (CR2) d. 7. Which of the following is true concerning Ag-induced B cell activation? a. Most antigens from tissue sites are transported to lymph nodes by afferent lymphatic vessels that drain into the subcapsular sinus of the nodes Antigens in immune complexes may bind to complemen type 2 or CR2) on marginal zone B cells, and these cells can transfer the immune complex-containing antigens to follicular B cells Polysaccharide antigens can be captured by macrophages in the marginal zone of splenic lymphoid follicles and displayed or transferred to B cells in this area All of the above b. t receptors (in particular the complement receptor c. d.Explanation / Answer
Ans 1 germinal centres - The follicles of the germinal epithelium give rise to rapidly dividing and multiplying B cells. The extrafollicular Helper T cells play an important role in selecting the B cells that go on to form specialised plasma proteins that are involved in an immune response. It also negatively selects potential autoimmune causing B cells.
Ans 2 Successful isotype switching and somatic hypermutation events. The AID enzyme generates mutations in DNA by deaminating the Cytosine base and thus converting it into a Uracil base. This means that a C:G base pair becomes a U:G mismatch. During replication, the U is recognized as a T and thus the Base pair is now converted to a T:A base pair.
Somatic hypermutation- This refers to the mutations that occur antibody genes to generate a library of antibody variants.
Isotype Switching - this is another process mediated by AID in which the Antibody switches a class. e.g IgM becomes IgA
Ans 3 Affinity maturation.
This is a process that occurs during an immune response. The T-cell dependent B cell undergoes mutation to have a greater affinity to the antigen and this is responsible for the heightened response observed when the same antigen is introduced into the body.
Ans 4 Early isotype switching and short-lived plasma cells. One might get confused with the second option. The second option is valid, as in that process occurs too. But the process of isotype switching occurs before the process of somatic hypermutation. The body needs a response for immediate protection and short-lived plasma cells provide that. The process of forming long-lived memory cells isn't as high on the priority list as that of the short-lived plasma cells.
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