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Which immunoglobulin is the largest in size?
A. IgA
B. IgD
C. IgE
D. IgM

Last updated date: 13th Jun 2024
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Hint: The immune system of our body protects us from foreign antigen like; bacteria and viruses. When any antigen is triggered by the immune system they release antibodies that bind to the antigen and lead them to destruction.

Complete Answer:
- The immunoglobulin is also termed as antibodies, the glycoprotein molecules that are formed by the white blood cells or plasma cells. They function as a critical part of the immune system by recognizing the antigen and binding with them and helping in their destruction.
- The immunoglobulin is a Y shaped protein that comprises fragment antigen-binding variable regions which we call Fab region. At the tip of an antibody, a paratope is found that is specific to a specific epitope on an antigen. It allows these two structures to bind together.
- The immunoglobulin is produced by the B cells of the adaptive immune system. The immunoglobulin has many classes like; immunoglobulin A, immunoglobulin G, immunoglobulin M, immunoglobulin D, and immunoglobulin E.
- Now, immunoglobulin M is a basic antibody secreted by B cells. It is the largest antibody in the circulatory system. It is the first antibody that formed in response to the exposure to an antigen and forms polymers. The IgM produces polymers where many immunoglobulin are covalently linked together by disulphide bonds mainly as pentameters. IgM has a molecular mass of 970kDa. The pentameric IgM has ten binding sites.

Thus, the correct option is ‘D’. IgM.

Note: The IgG is the antibody that neutralizes the toxicity of bacteria, binds antigens to increase the phagocytic activity, and triggers the complement protein system. The IgA is a principal antibody in secretion that bathes this mucosal surface.