Immunity

The secondary or anamnestic immune response is characterised by a faster, stronger, and more prolonged production of antibodies, predominantly of the IgG class, because memory B-cells generated during the first exposure quickly recognise the antigen and differentiate into plasma cells. On the very first encounter (primary response), IgM is the first antibody to appear, but in the secondary response the class switches and IgG dominates, providing high-affinity, long-lasting protection that forms the basis of vaccination. IgM is therefore incorrect for the secondary response, as it is the early, large pentameric antibody mainly tied to the primary response. IgE is wrong because it is associated with allergic reactions and defence against parasitic worms, not the bulk secondary antibody. IgA is also incorrect; it is the secretory antibody found in mucus, saliva, tears, and colostrum, guarding mucosal surfaces rather than dominating the secondary blood response. As outlined in NCERT Class 12, Chapter 8 (Human Health and Disease), immunological memory underlies the heightened secondary response exploited by booster vaccines. As a logical check, since memory cells trigger a rapid, high-titre, class-switched response, IgG is the only immunoglobulin matching all these features.