Abstract: Objective  To observe the immune response induced by ROP2 protein of Toxoplasma gonddi 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·d）] by subcutaneous injection three times at an interval of 2 weeks, respectively. Experimental mice were immunized with 100 μg ROP2 proteins, which were diluted to a final volume of 200 μl in PBS. On day 13, 27 and 41 after immunization, mice sera were collected for determination of antibody IgG and cytokine IFN-γ by ELISA. Two weeks after the final immuni-zation, 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 5×104 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-γ significantly increased in groups C ［（1 600.750±480.680） pg/ml］ and D ［（1 494.375±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-γ 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.

Key words: Toxoplasma gondii；Cimetidine, Rhpotry protein 2；Immune response；Protein vaccine