SURVIVAL OF IMMUNOGLOBULIN G-OPSONIZED TOXOPLASMA-GONDII IN NONADHERENT HUMAN MONOCYTES

Toxoplasma gondii is a protozoan parasite that is able to penetrate hu man monocytes by either passive uptake during phagocytosis or active p enetration. It is expected that immunoglobulin G (IgG) opsonization wi ll target the parasite to macrophage Fc gamma receptors for phagocytic processing and subsequent degradation, Antibody-opsonized T. gondii t achyzoites were used to infect nonadherent and adherent human monocyte s obtained from the peripheral blood of seronegative individuals. The infected monocytes were evaluated for the presence of intracellular pa rasites and the degree of parasiticidal activity. A marked difference in both the numbers of infected macrophages and numbers of parasites p er 100 macrophages was observed in the nonadherent cells when compared with those of the adherent cell population, When macrophage Fc gamma receptors were down-modulated, opsonized tachyzoites retained their ab ility to penetrate the host cell at a rate similar to that observed fo r unopsonized parasites. These results suggest that antibody opsonizat ion of T. gondii does not prevent active penetration of human monocyte s by the parasite and, furthermore, has little effect on intracellular replication of the parasite.