Which antibody is the first antibody secreted during the primary immune response to an antigen?

• A. IgA
• B. IgM
• C. IgE
• D. IgG

Answer: (B)

Verified step by step guidance

1. Understand the context of the question: it asks about the primary immune response, which is the body's first reaction to a new antigen.
2. Recall that during the primary immune response, B cells initially produce a specific class of antibody before class switching occurs.
3. Identify the antibody classes listed: IgA, IgM, IgE, and IgG, and recall their typical roles and timing in immune responses.
4. Remember that IgM is the first antibody produced by B cells during the primary immune response because it is expressed on the surface of naive B cells and secreted early before class switching.
5. Conclude that IgM is the first antibody secreted during the primary immune response, while other antibodies like IgG, IgA, and IgE appear later or in different immune contexts.