Mucosal And System Immune Responses Induced By Toxoplasma Gondii Antigens In Association With IFN-γ After Intranasal Immunization In BALB/c Mice

Toxoplasmosis is mainly disseminated by mucosa and placenta, second only malaria and schistosomiasis, but there is not an effective drug to prevent and treat it. Researching and developing the safe and effective vaccine against toxoplasma infection is the best strategy. At present, great attention was paid to the intranasal immunization that must have been the best effect. The aim of this study was to determine whether intranasal immunization with tachyzoite sonicated extract (TSo) plus IFN-γ were able to induce mucosal and system immune responses and to protect BALB/c mice orally challenged by T. gondii tachyzoites. Six-to 8-week-old BALB/c 100 mice were randomly divided into four groups, 25 mice per group, PBS group, 20μg TSo group, 500u IFN-γ group and 20μg TSo plus 500u IFN-γ group. Mice were intranasally immunized two times with an interval of two weeks. The ascites containing 4×104 tachyzoites of RH strain in each 0.5-ml dose were orally challenged to all animals on the 10 day the last immunization. Five mice in each group were killed on the day 7, 10, 13, 16, 19 after challenge, respectively. The content of IgA antibody in the sera, small intestinal secretions and feces were detected by ELISA, the changes of splenic CD4+ and CD8+ T lymphocytes were determined by SABC immunohistochemistry, the numbers of T. gondii tachyzoite were counted in the brains, lungs and livers.In the TSo+IFN-γ group, the contents of IgA antibody in sera, small intestinal secretions and feces were increase than that in others post infection (pi). The contents of IgA antibody in sera and feces of TSo+IFN-γ group were statistically higher than that of the PBS group on the day 7, 10 and the day 7, 13 pi, respectively. In the TSo+IFN-γ group, the percentages of splenic CD4+ T lymphocyte on the day 16, 19 pi were higher than that on the day 10 pi, and the percentages of splenic CD8+ T lymphocyte showed a higher level on the day 10, 13, 16, 19 pi, the CD4+/ CD8+ ratio was significantly reversed on the day 10, 13 pi. The numbers of tachyzoite in the brains, lungs and livers of the TSo+IFN-γ group decreased significantly than that of other groups pi. Compared with the PBS group and TSo+IFN-γ group, the numbers of tachyzoite in the brains decreased respectively 63.92%, 58.39% on the day 13, 19 pi.These results suggested that the effective humoral immunity responses were induced by intranasal immunization with TSo plus IFN-γ in mice, which produced the higher level of IgA antibody to play the major role against parasites at the local site. Intranasal immunization with TSo plus IFN-γ could stimulate the systemic immune reactions in mice, and improve the level of cellular immunity responses, and enhance the cytotoxicity of CD8+ T lymphocyte, and play an important part against T. gondii. Counting the numbers of tachyzoite in tissues is a better method to assess the protective against T. gondii.