Toxocara canis in mice: immune responses after infection and immunization

The proliferative response of spleen T and B lyrmphocytes, the percentage o f CD4+ and CD8+ T cells and the production of immunoglobulin subclasses of specific antibodies were studied in mice after their infection with eggs an d immunization with the excretory-secretory larva antigen of Toxocara canis . The proliferative activity of T aid B lymphocytes in mice C57BL6 was asse ssed spectrophotometrically, T subpopulation numbers were evaluated by flow cytometry and specific antibodies were detected by the ELISA method. The infection elicited long-term stimulation of the proliferative response of T and B cells. Re-infection significantly increased the activity of thes e cells. Though there was a rapid increase in the proliferative response of T-cells after mouse immunization, re-immunization caused its decrease. B l ymphocytes responded more intensively after re-immunization than after immu nization. The infection caused a decrease in CD4+ T-cells only up to day 21 of the experiment, followed by an increase. In comparison with the CD4+ ce ll population, the percentage of CD8+ T-cells was not influenced up to day 21 of the experiment. Re-infection significantly reduced the representation of both subpopulations of T-cells. Immunization caused a long-term inhibit ion of the percentage occurrence of both the subpopulations for the duratio n of the experiment and, moreover, re-immunization enhanced this decrease. The infection elicited a significantly increased production of immunoglobul in IgG(1) and IgG(2) subclasses, with IgG(2) dominancy and with an increase in both the subclasses after the reinfection. The immunization and re-immu nization did not induce the production of IgG(1) but even the production of IgG(2) was very low. The results indicate that after the infection, when a host body is exposed to the influence of various larval antigens, its immune response is more in tensive than after its re-immunization with the excretory-secretory antigen alone.