Mineo J R, McLeod R, Mack D, Smith J, Khan I A, Ely K H, Kasper L H
Department of Medicine, Dartmouth Medical School, Hanover, New Hampshire 03756.
J Immunol. 1993 May 1;150(9):3951-64.
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.
针对刚地弓形虫主要表面抗原（SAG-1，P30）的单克隆抗体和多克隆单特异性抗体可抑制人成纤维细胞和鼠肠上皮细胞的感染。从针对P30的多克隆单特异性抗体制备的Fab片段对入侵也有这种抑制作用，这表明该抗体直接阻断寄生虫对宿主细胞的感染，而不是使寄生虫凝集。针对另一种表面蛋白（P22）的抗体不会改变体外感染情况。如果针对P30的抗体的抑制作用是由于空间位阻或与P30相邻的表面表位的复合作用，那么针对其他表面表位的抗体也会具有抑制作用，但实际并非如此。用尿素处理抗体（这可区分高亲和力和低亲和力抗体）不会改变抗P30抗体的作用。这一观察结果表明，针对P30的抗体的作用并非是由于针对P22和P30的抗体在亲和力上存在差异而产生的假象。用感染了RH或PTg株刚地弓形虫（P30+）的小鼠的热灭活抗血清，当用同源野生型寄生虫攻击时，分别可抑制成纤维细胞感染87%和40%。相比之下，这些抗血清对P30缺陷型突变体（PTgB）感染人成纤维细胞的抑制作用很小（分别为13%和19%）。针对P30缺陷型突变体制备的抗血清对具有表面P30的野生型菌株感染细胞没有显著影响。新糖蛋白BSA-葡糖酰胺能竞争性阻断具有表面P30的P30+速殖子对人成纤维细胞的感染，其阻断水平高于没有表面P30的速殖子。这一观察结果表明，可能存在一种糖基化的宿主细胞受体，刚地弓形虫的主要表面抗原SAG-1（P30）可与之结合。经口感染的小鼠会产生针对刚地弓形虫主要30 kDa表位的肠道IgA抗体。因此，刚地弓形虫的主要表面表位SAG-1（P30）在刚地弓形虫感染宿主细胞过程中具有重要的功能作用，并且在经口感染后会引发肠道抗体反应。
