Clinical Laboratory Science Immunology Practice Test 2026 – Your All-in-One Guide to Exam Success!

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.