Effect of macrophage activation on phagocyte-Plasmodium interaction

We investigated the effect of both immune and normal sera on the binding of free Plasmodium berghei by resident and activated macrophages. Resident macrophages bound plasmodia to a greater extent than did activated macrophages, regardless of treatment. Resident macrophages bound free plasmodia, predominantly trophozoites, in the presence of normal serum by a mechanism inhibited by N-acetylglucosamine and N-acetylmannosamine. Macrophages activated through treatment with Propionibacterium acnes ("Corynebacterium parvum"), on the other hand, did not bind free plasmodia in the presence of normal serum through systems inhibited by N-acetylmannosamine or N-acetylglucosamine. The binding of free plasmodia by activated macrophages was greatest in the presence of immune serum and could be inhibited by immune complexes but not by N-acetylmannosamine or N-acetylglucosamine. These results suggest that a receptor for a carbohydrate component of a normal serum opsonin mediates initial adherence of plasmodial antigen onto resident macrophages, triggering both the immunological cascade and macrophage activation. After activation, the macrophages no longer have the carbohydrate-specific receptor but do have functional Fc receptors which mediate the adherence of immune-serum-opsonized plasmodia.