Positive evidence that anti- Toxoplasma gondii IgA antibody exists in the intestinal tract of infected cats and exerts protective activity against the infection

The presence of anti- Toxoplasma gondii IgA antibody in the feces and intestinal tract of cats infected with this parasite was demonstrated using an immunoblotting assay. Cats ( n = 5) were inoculated orally with T. gondii cysts and supernatants of feces and washings of the intestinal tract were assayed for secretory IgA specific for the parasite. The secretory IgA detected recognized tachyzoite antigens of m.w. 24, 34, 38 and 43 kDa and one sporozoite antigen of m.w. 24 kDa. No reactivity was shown against bradyzoites or enteroepithelial stage parasites. Tachyzoites preincubated with washings of the intestinal tract of infected cats showed decreased activity in penetration of feline fibroblast cells, as compared to tachyzoites preincubated with similar derived from non-infected cats. The addition of either anti-cat IgA or anti-cat IgG to the washings had no effect on the inhibitory activity which reduced the parasite's cell-penetration activity. However, the addition of both anti-cat IgA and anti-cat IgG to the washings diminished the inhibitory activity. These results suggest that anti- T. gondii antibodies of both classes, secretory IgA and IgG, exist in the intestinal tract of infected cats and these may be capable of preventing infection.