After exposure to antigen, the first antibodies detectable belong to which class?

After exposure to antigen, the first antibodies detectable belong to which class?

• A. IgA
• B. IgE
• C. IgG
• D. IgM

Answer: (D)

In a primary immune response, the first antibodies you detect are IgM. This happens because naive B cells initially produce and secrete IgM before undergoing class switching. IgM is a pentamer, giving it high avidity that helps bind multivalent antigens effectively and activate the classical complement pathway, providing a rapid first line of defense. Over time, with T-cell help and germinal center reactions, B cells switch to other isotypes such as IgG, IgA, or IgE, which appear later as the response matures. So IgM stands out as the earliest detectable antibody after initial antigen exposure.

In a primary immune response, the first antibodies you detect are IgM. This happens because naive B cells initially produce and secrete IgM before undergoing class switching. IgM is a pentamer, giving it high avidity that helps bind multivalent antigens effectively and activate the classical complement pathway, providing a rapid first line of defense. Over time, with T-cell help and germinal center reactions, B cells switch to other isotypes such as IgG, IgA, or IgE, which appear later as the response matures. So IgM stands out as the earliest detectable antibody after initial antigen exposure.