I read that opsonins are a type of antibody that play a vital role in chemotaxis and phagocytosis in general. The fact of them being antibodies though, got me confused. Antibodies are, to my knowledge (however inadequate it may be) , released by plasma cells after macrophages present antigens. Yet my book says that pathogens are covered in antibodies (opsonin) which help the macrophage initiate phagocytosis. How can antibodies (opsonin) be present before the APC Present the antigens to activate the production of antibodies?
P.S.: I'm a college student so there's probably a lot of things I'm missing out on. Please do fill me in :)