Antibodies to Toxoplasma gondii major surface protein (SAG-1, P30) inhibit infection of host cells and are produced in murine intestine after peroral infection.

Abstract

Monoclonal and polyclonal, monospecific antibodies to the major surface antigen of Toxoplasma gondii (SAG-1, P30) inhibit infection of human fibroblasts and murine enterocytes. Fab prepared from polyclonal, monospecific antibody to P30 also have this inhibitory effect on invasion, which indicates that this antibody directly blocks parasite infection of host cells rather agglutinating the parasite. Antibodies to another surface protein (P22) did not alter in vitro infection. If the inhibitory effect of antibody to P30 was due to steric hindrance or complexing of surface epitopes contiguous to P30, antibodies to other surface epitopes would also be inhibitory and they are not. Urea treatment of antibody (which permits discrimination of high and low avidity antibody) did not alter the effect of anti-P30 antibody. This observation indicates that the effect of the antibody to P30 was not an artifact of differences in the avidity of the antibody to P22 and P30. Heat inactivated antisera from mice infected with either RH or PTg strain T. gondii (P30+) inhibit infection of fibroblasts when challenged with autologous wild-type parasites by 87 and 40%, respectively. In contrast, these antisera have little inhibitory effect (13 and 19%, respectively) against infection of human fibroblasts by a P30-deficient mutant (PTgB). Antisera raised to the P30-deficient mutant had no significant effect on infection of cells by wild-type strains that have surface P30. The neoglycoprotein, BSA-glucosamide, competitively blocks infection of human fibroblasts by P30+ tachyzoites with surface P30 in higher level than those without surface P30. This observation indicates that there is likely to be a glycosylated host cell receptor to which T. gondii's major surface Ag SAG-1 (P30) binds. Mice infected perorally develop intestinal IgA antibody to the major 30-kDa epitope of T. gondii. Thus, the major surface epitope of T. gondii, SAG-1 (P30), has an important, functional role in infection of host cells by T. gondii and elicits an intestinal antibody response after peroral infection.

P25 and P28 proteins of the malaria ookinete surface have multiple and partially redundant functions

“…None of our assays has revealed a functional difference between p25 and p28 Sko parasites; this implies that the encoded proteins are redundant. Interestingly, functional redundancy has been described for the various GPI‐anchored, cysteine‐rich surface proteins of the SAG multigene family in the related apicomplexan parasite T.gondii (Mineo et al ., 1993). Like P25 and P28, antibodies to SAG1 inhibited parasite interaction with host tissues, yet SAG1 ‐deficient parasites were invasive, as were SAG3 ‐negative parasites.…”

“…Anopheles gambiae was used because in this species innate immune responses have been de®ned which can be used as markers for the process of crossing the epithelium by P.berghei ookinetes (Dimopoulos et al, 1997(Dimopoulos et al, , 1998. In addition, a refractory strain of A.gambiae encapsulates and melanizes ookinetes in the BL region of the epithelium after crossing the epithelium and as they emerge into the extracellular space (Paskewitz et al, 1988). Unlike normal ookinetes, these melanized ookinetes can easily be detected.…”

Stable endocytic structures navigate the complex pellicle of apicomplexan parasites

“…The T. gondii surface protein SAG1 is taken up through endocytosis in extracellular tachyzoites 31 so we targeted this molecule to develop a new endocytosis assay for parasites within the host cell vacuole. Previous assays for endocytosis of SAG1 in extracellular parasites used antibodies targeting SAG1 31 but these antibodies are known to also inhibit invasion 49 and, therefore, are incompatible with the analysis of intracellular parasites. Instead, we modified the sag1 gene to express a fused HaloTag that can catalyze covalent linkage to exogenous fluorescent ligands 50 .…”

Nano-Encapsulated Antioxidant: Retinoic Acid as a Natural Mucosal Adjuvant for Intranasal Immunization against Chronic Experimental Toxoplasmosis

“…Several pieces of evidence support the association of antibodies in the defense against pathogens using diverse methods, such as inhibiting the attachment to host cells [ 48 ]. Much of the literatures has shown that Toxoplasma -specific antibodies can block the in vitro penetration of enterocytes by tachyzoites [ 49 , 50 , 51 ]. Thereby, in the current study, the capability of the harvested sera from mice two weeks following the completion of different immunization regimens to prevent in vitro parasite invasion was assessed.…”