Original antigenic sin has implications for immune responses to related antigens; which statement best captures its impact?

• A. Original antigenic sin can cause suboptimal responses to new related antigens due to reliance on prior memory.
• B. It ensures optimal responses to all future related antigens.
• C. It has no effect on how the immune system responds to related antigens.
• D. It only affects T cell responses, not B cell responses.

Answer: (A)

Original antigenic sin describes how the immune system tends to react to a related but distinct antigen by reactivating memory B cells from the first exposure. Those memory cells produce antibodies targeting the original epitopes, biasing the response toward familiar features. As a result, the body may generate fewer new antibodies against the novel epitopes on the related antigen, leading to a suboptimal or less effective response. This phenomenon shows how prior experience can shape future responses rather than guaranteeing optimal protection against related strains. The effect centers on antibody-producing B cells; while T cells can be involved in broader immunity, the key impact here is on humoral memory.