[Study on immune response in BALB/c mice induced by ROP2 protein of Toxoplasma gondii with cimetidine].

Objective: To observe the immune response induced by ROP2 protein of Toxoplasma gondii with cimetidine in mice.

Methods: Eighty BALB/c mice were randomly divided into 4 groups: PBS (group A), ROP2 protein (group B), ROP2 protein-Freund's adjuvant (group C) and ROP2 protein-cimetidine (group D). Mice were immunized with PBS, ROP2 protein, ROP2 protein and Freund's adjuvant, ROP2 protein and cimetidine [200 mg/(kg x d)] by subcutaneous injection three times at an interval of 2 weeks, respectively. Experimental mice were immunized with 100 microg ROP2 proteins, which were diluted to a final volume of 200 microl in PBS. On day 13, 27 and 41 after immunization, mice sera were collected for determination of antibody IgG and cytokine IFN-gamma by ELISA. Two weeks after the final immunization, T cells subpopulation was detected by flow cytometry and splenocyte proliferation activity was determined with CCK-8. Another 12 immunized mice in each group were intraperitoneally challenged with 5 x 10(4) tachyzoites of T. gondii and the survival time was observed.

Results: Two weeks after final immunization, compared with groups A [(659.750 +/- 239.962) pg/ml] and B [(872.750 +/- 197.011) pg/ml], the level of IFN-gamma significantly increased in groups C [(1 600.750 +/- 480.680) pg/ml] and D [(1494.375 +/- 451.655) pg/ml] (P < 0.01). Similarly, compared with groups A (0.636 +/- 0.108) and B (0.871 +/- 0.089), the level of IgG was also higher in groups C (1.068 +/- 0.111) and D (1.046 +/- 0.147) (P < 0.01). The proliferation of splenocytes rose in group C (0.831 +/- 0.130) after immunization, and similarly in group D (0.762 +/- 0.089), and were both significantly higher than that of groups A (0.504 +/- 0.078) and B (0.592 +/- 0.160) (P < 0.01). Moreover, ratio of CD4+/CD8+ in groups C (0.831 +/- 0.130) and D (0.762 +/- 0.089) were higher than that of groups A (0.504 +/- 0.078) and B (0.592 +/- 0.160) (P < 0.05). After challenge with violent virulence strain of tachyzoites, the median survival time of mice in groups A, B, C, and D were 96, 108, 132, and 132 h, respectively. The mean survival time of mice in groups C and D were longer than that of groups A and B (P < 0.05). There was no significant difference in 5 parameters between C and D: the level of IFN-gamma and IgG, CD4+/CD8+ ratio, splenocyte proliferation, and survival time of mice (P > 0.05).

Conclusion: Cimetidine can enhance the humoral and cellular immune response induced by ROP2 protein.