Question

Changes in Ig genes during B cell's life:
isotype switch

Answer 1

Isotype switching is a process where B cells initially producing IgM switch to producing other antibody classes like IgG, IgA, or IgE while retaining the specificity for the original antigen. This is achieved through genetic rearrangement of the constant region of Ig genes. The generation of diverse antibodies with unique variable regions is essential for the adaptive immune response.

Step-by-step explanation:

The process known as isotype switching refers to changes in the immunoglobulin (Ig) genes during a B cell's life. Initially, B cells produce and secrete pentameric IgM, which is a type of antibody. Later, under the influence of cytokines secreted by helper T cells (T² cells), plasma cells derived from the B cells switch from producing IgM to other classes like IgG, IgA, or IgE. This class switching is made possible by genetic rearrangements, specifically in the constant region of the Ig genes, which changes the antibody's class but retains its original epitope specificity due to the unchanged variable region.

The genetic diversity in B cells arises from the recombination of various V (Variable), D (Diversity), and J (Joining) gene segments during B cell maturation. The resulting antibodies have a vast array of unique variable regions capable of binding different antigens. The constant domain, not part of the variable region, is identical across all antibodies of a particular class, dictating the antibody's class-specific functions. The resulting antigen-specificity allows antibodies to bind specifically to antigens, which is crucial for the adaptive immune response.

Answer 2

The statement "changes in Ig genes during B cell's life: isotype switch" is true.

Step-by-step explanation:

The changes in immunoglobulin (Ig) genes during a B cell's life include a process known as isotype switching. Initially, B cells express B cell receptors (BCRs) and secrete pentameric IgM antibodies.

Through the influence of cytokines secreted by T-helper cells, plasma cells can undergo class switching to produce different classes of antibodies such as IgG, IgA, or IgE that have the same epitope specificity but different constant regions resulting from genetic rearrangement of gene segments encoding the constant region. Variable regions remain unchanged, ensuring that the new antibody retains its original antigen-binding ability.

Germ-line B cells use a DNA recombinase enzyme to randomly excise and rearrange V (Variable), D (Diversity), and J (Joining) segments to create a unique binding region for antigens. Such gene rearrangements enhance the B cell's ability to produce a diverse range of antigen-specific receptors. After activation, these cells can differentiate into plasma cells, capable of secreting high quantities of antibodies that possess a unique variable region formed by this genetic rearrangement process.

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True/False: changes in Ig genes during B cell's life:

isotype switch