Which immunoglobulin is the first antibody produced during a primary immune response?

Which immunoglobulin is the first antibody produced during a primary immune response?

• A. IgG
• B. IgM
• C. IgA
• D. IgE

Answer: (B)

In a primary immune response, the first antibody produced is IgM. When naive B cells first encounter an antigen, they typically secrete IgM (and express it as their surface B-cell receptor) before undergoing any class switching. The IgM produced is often a pentamer, which makes it especially good at clumping pathogens together (agglutination) and efficiently activating the classical complement pathway to help clear infection early. Over time, with T cell help and germinal center reactions, B cells undergo class switch recombination to produce other isotypes such as IgG, IgA, or IgE, which take over in the later stages or in mucosal and allergic contexts. That’s why IgG, IgA, and IgE are not the first antibodies in a primary response.

In a primary immune response, the first antibody produced is IgM. When naive B cells first encounter an antigen, they typically secrete IgM (and express it as their surface B-cell receptor) before undergoing any class switching. The IgM produced is often a pentamer, which makes it especially good at clumping pathogens together (agglutination) and efficiently activating the classical complement pathway to help clear infection early. Over time, with T cell help and germinal center reactions, B cells undergo class switch recombination to produce other isotypes such as IgG, IgA, or IgE, which take over in the later stages or in mucosal and allergic contexts. That’s why IgG, IgA, and IgE are not the first antibodies in a primary response.