Opsonization of Toxoplasma gondii tachyzoites with nonspecific immunoglobulins promotes their phagocytosis by macrophages and inhibits their proliferation in nonphagocytic cells in tissue culture

Abstract

We have recently shown that Toxoplasma gondii tachyzoites grown in in vitro culture can bind unspecific immunoglobulin (Ig) through their Fc moiety. We show now that Fc receptors are also present on T. gondii within the host animal, and that intraperitoneal parasites in immunocompetent mice are saturated with unspecific Ig. We have also investigated the effect of the parasite's Fc receptor on the interaction of tachyzoites with mammalian cells, using the Vero cell line as a model for nonphagocytic host cells and murine peritoneal macrophages in primary culture as a model for phagocytic cells. Coating of tachyzoites with parasite-unrelated Ig did not enhance their invasive capacity in either target cell type, but slightly decreased the parasite proliferation. Moreover, phagocytosis by macrophages was increased by approximately 50% when parasites were coated with unspecific Ig. These results indicate that the Fc receptor on T. gondii affects the balance between invasion and phagocytosis in a way that is detrimental to the parasites.

Toxoplasma gondii: Ultrastructural localization of specific antigens and inhibition of intracellular multiplication by monoclonal antibodies

“…The Fc receptor on T. gondii affects the balance between invasion and phagocytosis (Vercammen et al, 1999). When Toxoplasma are treated with specific mAb before infection, the ability of parasite to multiply reduces in murine macrophage (Hauser and Remington, 1981;Mineo et al, 1994;Vercammen et al, 1999). In this experiment, the invasion of T. gondii tachyzoites into mouse peritoneal macrophage was inhibited after the pretreatment of polyclonal immune serum, mAb M110 and M110, M556, R7A6 and M621 mixed mAbs.…”

“…Binding of antibody-opsonized parasite to the host cell FcR receptors triggers phagocytosis and the parasite is internalized to the phagosome (Fadul et al, 1995). The Fc receptor on T. gondii affects the balance between invasion and phagocytosis (Vercammen et al, 1999). When Toxoplasma are treated with specific mAb before infection, the ability of parasite to multiply reduces in murine macrophage (Hauser and Remington, 1981;Mineo et al, 1994;Vercammen et al, 1999).…”

Toxoplasma gondii-Specific Immunoglobulin M Limits Parasite Dissemination by Preventing Host Cell Invasion

“…The results showed that tachyzoites derived directly from 2-day-infected mice had the capacity to activate the complement cascade (Fig. 5A), possibly a result of nonspecific antibody binding to the parasite surface (43). Nevertheless, parasites obtained from WT and IgM Ϫ/Ϫ mice were similarly able to activate the classical complement cascade, and incubation of parasites with WT and IgM Ϫ/Ϫ nonimmune serum did not enhance parasite killing above the direct ex vivo level witnessed when parasites were incubated with PBS (Fig.…”

“…Thus, antibodies are required for effective vaccination against virulent RH challenge (37) and in the prevention of toxoplasmic encephalitis during chronic infection (21,23). Opsonization of tachyzoites with specific and nonspecific antibodies may also enhance neutrophil toxoplasmastatic activity, prevent the suppression of macrophage proinflammatory cytokine production, and increase phagolysosomal fusion and parasite killing of macrophages (4,7,24,43). In vitro experiments have shown that antibodies to T. gondii apical membrane antigen 1 (AMA-1) and the major tachyzoite surface antigens, SAG-1 and SAG-2, can inhibit cellular invasion (14-16, 28-30, 42) and activate the complement cascade, which can kill tachyzoites (11,39).…”

Virus-Like Nanoparticle Vaccine Confers Protection against Toxoplasma gondii

“…T . gondii can be killed by activated complement system or phagocytosis and macrophage killing [18–20]. To induce mucosal immunity, intranasal vaccination was applied.…”