This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “T-Dependent B-Cell Responses – Somatic Hypermutation and Class Switching”.
1. Where does antibody class switching occur?
a) Immature B cells
b) Mature B cells
c) T cells
d) Th1 cells
View Answer
Explanation: Antibody class switching occurs in mature B cells and it responds to antigen stimulation and costimulatory signals. It occurs by a type of mechanism which is associated with intrachromosomal deletional recombination. This class switching mechanism occurs within G-rich tandem repeated DNA sequences.
2. How much region of antibody is targeted by Ig hypermutation?
a) 1kb
b) 2.5kb
c) 1.5kb
d) 10kb
View Answer
Explanation: Ig hypermutation eventually targets an antibody region of about 1.5 kb. This antibody region contains of 2 important regions – 1) the V (variable), D (diversity) and J (joining) region (also denoted as V(D)J) and 2) a part of the association of J(joining) and C (constant) region (denoted as JC intron).
3. Immunoglobulin class switching is also termed as class switch recurring recombination.
a) True
b) False
View Answer
Explanation: Immunoglobulin class switch is also known as class switch recombination (denoted as CSR). It is also known by different terms like isotype switching and isotypic commutation. It is a DNA recombination process which carries out the replacement of immunoglobulin region that can protect against the pathogenic infections.
4. What is a centrocyte?
a) B cell with 2 nuclei
b) Minor population of tumour
c) B cell with cleaved nucleus
d) B cell with basophilic nucleoli
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Explanation: A centrocyte is defined as the stage of B cell development which shows an appearance of a cleaved nucleus. When it undergoes positive selection and isotype switching, it either carries forwards to become a memory cell or plasma cell. Centrocytes have a high affinity for antigen. They force the antigen to undergo isotype switching due to which there is a replacement of IgM antibodies with IgG, IgA or IgE.
5. What does AID stand for in terms of antibody class switching?
a) Activation-induced cytidine deaminase
b) Activation-induced cytokine deaminase
c) Antibody-induced cytidine deaminase
d) Antibody-induced cytokine deaminase
View Answer
Explanation: AID stands for activation-induced cytidine deaminase. It initiates B cell-specific recombination which deaminates cytosines in donor as well as acceptor. Antibody class switching occurs by certain type of deletional recombination mechanism. AID activity converts some of the bases to other bases (associated with the S region of G-rich DNA sequences). For example: conversion of dS bases to dU bases.
6. Which part of the antibody molecule does class switching affect?
a) Fc portions
b) Fab fragment
c) Paratope
d) Light chain portion
View Answer
Explanation: Class switching mainly affects the Fc fragment portions as well as the constant portions of heavy chains of antibody. Antibodies are found in a general Y shaped arrangement, with two heavy and two light chains. The light chains are each made up of a constant and variable region. Each of the heavy chains is made up of a variable region, and three constant segments. The variable regions of the heavy and light chains come together to form two identical paratopes for antigen binding. The constant heavy chain segment create the Fc region, which is vital for binding to Fc receptors on other cell types and mediating antibody functions.
7. From where are Ramos B cells derived?
a) Human Burkitt’s lymphoma
b) Mice spleen
c) Human spleen
d) Mammalian bone marrow
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Explanation: Ramos B cells are derived from human Burkitt’s Lymphoma. These cells have similar characteristics as that of B lymphocytes. These cells are widely used as model for apoptotic studies. The cell line obtained from Ramos B cell is also used for studying the DNA lesions. To study the morphological features of Ramos B cell line, suspension cell culture is used as a primary practice to obtain a perfect cell line.
8. According to the recent study, which of the following link was detected in a chicken B cell line?
a) Ig hypermutation and IgV region
b) IgV region and Ig gene
c) Ig hypermutation and Ig gene
d) IgV region and DNA recombinants
View Answer
Explanation: Current researches and studies have shown that there is a connection between Ig hypermutation and Ig gene. This was first seen to be studied in chicken B cell line. This was found out on the basis of hypermutation process which showed breakage of DNA fragments. This link between hypermutation and Ig gene was seen active in IgV region of antibody. This entire theory was further studied by scientists like Sale and his colleagues.
9. During class switch recombination, which portion of antibody gets deleted?
a) Antibody-light chain locus
b) Antibody-heavy chain locus
c) Antibody-Fc fragment
d) Antibody-Fab fragment
View Answer
Explanation: Class switching occurs by a mechanism called class switch recombination (CSR) binding. During CSR mechanisms, some small portions of antibody that possess heavy chain locus get deleted and eliminated from the chromosome. However, the characteristic gene segments are forced to re-join in order to take the place of deleted locus. This event occurs so that the antibody gene maintains its functionality even after the elimination takes place.
10. Immunoglobulin class switching within intestine may be directed towards which of the following antibody isotype other than IgA?
a) IgG and IgM
b) IgG and IgD
c) IgE and IgM
d) IgG and IgE
View Answer
Explanation: Immunoglobulin class-switch mechanism that takes place within the intestine is associated and directed towards IgA. However, in the presence of certain cytokines, isotype IgA is forced to shift toward IgG or IgE. In such cases, high inflammation occurs due to which TH1 and TH2 cytokines control the commitment of naïve B cells towards IgE and IgG. This results in production of plasma cells.
Sanfoundry Global Education & Learning Series – Immunology.
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