Microbiology Practice Exam

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What is the structure of Immunoglobulin D (IgD)?

Dimetric
Monomer
Polymer
Trimer

The correct answer is: Monomer

Immunoglobulin D (IgD) is characterized as a monomer, which means that it is composed of a single unit of immunoglobulin. This structure allows IgD to have a unique role in the immune system, primarily in B-cell activation and regulation. Unlike other immunoglobulin classes, IgD is not typically found in large quantities in the bloodstream; instead, it is predominantly expressed on the surface of naïve B cells as part of their receptor complex. The monomeric structure of IgD contrasts with other immunoglobulins that may form multimeric complexes. For example, IgM exists as a pentamer in its functional form, while IgA can be found as a dimer. The single-unit form of IgD allows it to efficiently engage with antigens and interact with other receptors on B cells, facilitating the immune response to pathogens. Understanding the monomeric nature of IgD is crucial for comprehending its specific functions within the immune system.