Which immunoglobulin can be elevated in secondary responses and confers long term immunity or be deficient in immunodeficiencies?

• A. IgG
• B. IgM
• C. IgA
• D. IgE

Answer: (A)

In a secondary immune response, memory B cells are rapidly reactivated and produce antibodies with high affinity, and the major isotype that drives this rapid, long-lasting protection is IgG. This class-switching to IgG provides durable systemic immunity through efficient opsonization, neutralization, and activation of the complement system. IgG’s ability to persist in circulation and its versatility in defending against pathogens make it the hallmark of a robust memory response and long-term immunity. Immunodeficiencies involving IgG lead to recurrent infections, highlighting its central role in sustained protection.

IgM is the first antibody produced in a primary response and has lower affinity; it’s less about lasting immunity and more about the initial defense. IgA mainly protects mucosal surfaces with secretory IgA, and IgE is involved in allergic responses and defense against parasites, not the principal mediator of long-term systemic memory.