Abstract： Objective To investigate the allograft immune hyporesponsiveness induced by complement regulatory protein Crry as well as CD4+ T lymphocytes involved.Methods CD4+ T cells were isolated from spleens of C57BL/6 mice by magnetic-activated cell sorting, and CD4+ T cell proliferation was induced by anti-CD3, anti-CD28, anti-Crry, co-stimulations of anti-CD3/anti-CD28, anti-CD3/anti-Crry, or the monoclonal antibody panel against CD3/CD28/Crry.Production of interleukin-2 (IL-2), γ-interferon (γ-IFN), interleukin-10 (IL-10) and interleukin-4 (IL-4) was detected in the supernatants of different groups.Allo-MLR was examined by MTT colorimetry with spleen cells from BALB/c mice as the stimulators and spleen cells of C57BL/6 mice as responders.Results Compared with CD3 group, CD3/CD28, CD3/Crry and CD3/CD28/Crry co-stimualtion all could significantly induce more proliferation (P<0.05).CD3/CD28/Crry co-stimulation significantly increased the proliferation compared with CD3/CD28 or CD3/Crry co-stimulation (P<0.05).IL-2 and γ-IFN levels were significantly increased in CD3/CD28 co-stimulation as compared with CD3 or CD28 or Crry or CD3/Crry group (P<0.05).IL-4 levels were significantly increased in CD3/Crry co-stimulation as compared with CD3 or CD28 or Crry or CD3/CD28 groups (P<0.05).There was no significant difference in IL-10 level among the different groups (P>0.05).CD3/Crry co-stimulation significantly inhibited proliferation in mixed lymphocyte culture (P<0.05).Conclusion Complement regulatory protein Crry induces IL-4 in CD4+ T ceils, suppresses IL-2 and γ,-IFN production, and induces allograft immune hyporesponsiveness