Which antibody is first secreted when an antigen is encountered for the first time?

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Multiple Choice

Which antibody is first secreted when an antigen is encountered for the first time?

In a primary immune response, the first antibody produced is IgM. Naive B cells encounter the antigen and, with help from T cells, differentiate into plasma cells that secrete IgM as the initial antibody. IgM is a pentamer, giving it high valency to effectively agglutinate pathogens and readily activate the complement system. After this initial wave, B cells can undergo class switch recombination under cytokine signals to produce other isotypes—IgG, IgA, or IgE—depending on the immune context. IgG becomes more prominent later and provides long-term systemic immunity, IgA operates mainly at mucosal surfaces, and IgE is involved in allergic responses and antiparasite defense.

In a primary immune response, the first antibody produced is IgM. Naive B cells encounter the antigen and, with help from T cells, differentiate into plasma cells that secrete IgM as the initial antibody. IgM is a pentamer, giving it high valency to effectively agglutinate pathogens and readily activate the complement system. After this initial wave, B cells can undergo class switch recombination under cytokine signals to produce other isotypes—IgG, IgA, or IgE—depending on the immune context. IgG becomes more prominent later and provides long-term systemic immunity, IgA operates mainly at mucosal surfaces, and IgE is involved in allergic responses and antiparasite defense.

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