Objective:To observe the correlation between the B7 blocker,CD28 and cytotoxic T lymphocyte-associated antigen 4 immunoglobulin (CTLA-4Ig) impacting on Th17 and Treg cells expressed in the spleen of lupus mice and its intervention role in lupus-like symptoms of B6.MRL-Faslpr/J lupus mice.Methods:Sixteen 4-month-old female B6.MRL-Faslpr/J mice were selected and randomly divided into treatment group ( groupⅠ) and control group ( groupⅡ);injected the same amount of CTLA-4Ig and PBS intra-venously,checked their 24 hour urine protein ,ANA antibody,ds-DNA antibodies before and after the intervention.Two weeks after the intervention ,detected serum IL-17A,and the percentage of Th17 and Treg cells in their spleen.Results:Two weeks after the last inter-vention,24-hour urine protein,serum ANA and ds-DNA in groupⅠdecreased,and all the differences were statistically significant (P<0.05) compared with groupⅡ.Two weeks after the last intervention,serum IL-17A and the proportion of Th17 cells in the spleen in groupⅠwere lower than those in groupⅡ, but Treg cells in CD4+T lymphocytes was higher than that in groupⅡ,all the differences were statistically significant ( P<0.05).Conclusion:CTLA4-Ig can relieve the lupus-like symptoms in lupus mice;raising the number of Treg cells and decreasing the number of Th17 cells may be one of the important mechanisms for CTLA-4Ig to alleviate lupus-like symptoms in B6.MRL-Faslpr/J mice.