Original antigenic sin refers to which immunological phenomenon?

• A. The immune system tends to rely on memory of the first encounter with a related antigen, shaping responses to later related antigens.
• B. Original antigenic sin describes immune memory that fails with every new exposure.
• C. It describes enhanced responses to unrelated antigens.
• D. It is the tendency to ignore memory responses to related antigens.

Answer: (D)

Original antigenic sin is the tendency of the immune system to rely on memory from the first encounter with a related antigen, shaping responses to later related antigens. When a person is later exposed to a similar pathogen, the immune system reactivates the memory B cells generated during the initial infection and tends to produce antibodies targeting epitopes shared with the original antigen. This can bias the response toward those familiar epitopes and sometimes limit the generation of new antibodies against novel epitopes on the newer antigen, potentially reducing effectiveness against drifted strains. It’s not about responses to unrelated antigens, nor about memory failing entirely, nor about ignoring memory responses—the phenomenon is about directing the response based on the first encounter with a related antigen.