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I have a conceptual misunderstanding relating to immunology which I'd be grateful if anyone could help me clear up.

My A Level textbook says that at the start of an immune response, opsonins bind to antigens; these opsonins are "a type of antibody" that then increase the probability of the pathogen being phagocytosed by a macrophage or neutrophil.

Macrophage phagocytosis then leads to antigen presentation; the macrophage migrates to the lymph node and then the hope is that a lymphocyte with the specific receptor binds to the antigen on the macrophage APC. Clonal selection/expansion/differentiation follows, and the B plasma cells produce large amounts of antibody that are released into the blood.

But why is this necessary, if the opsonins at the start of the process which tagged the pathogen for phagocytosis already exist in the body at the start of the response, before clonal selection? What can the very specific lymphocyte-produced antibodies do that the more generic opsonins can't?

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