Opsonization-enhanced phagocytosis of foot-and-mouth disease virus.

Using isolated peritoneal adherent cells, in which monocytes and macrophages dominate, the uptake and destruction of foot-and-mouth disease virus (FMDV) was enhanced by the opsonization with mAb of particular epitope specificity. This was seen under conditions in which virus infectivity was not neutralized, as determined by in vitro assay. Activation of macrophages in vivo further enhanced the uptake of opsonized virus, presumably by increasing the percentage of phagocytosing cells. The enhanced phagocytosis required opsonization and apparently made use of FcR+ cells, because pepsin-treated antibodies and separated F(ab')2 fragments did not enhance the capacity of the peritoneal cells to react with the virus. The reaction also relied on active phagocytosis, because inhibition of phagocytosis using silica interfered with the binding of both virus alone and virus/antibody complexes. This evidence shows that the previous in vivo observations (McCullough et al., 1986b) of enhanced protection by the mAb can be related to active phagocytosis of virus and virus/antibody complexes. The reaction is not passive adsorption to the monocyte surface, but an active phagocytosis of the virus or the complex.