Abstract： Objective To study the effects of cryopreservation on the immunogenicity of human umbilical vein endothelial cells(HUVEC).Methods HUVEC were isolated ex vivo and cryopreserved.Lymphocyte stimulation index(SI)was analyzed by MTT in lymphoeyte-endothelial cell co-culture.Both HLA-ABC and HLA-DR antigen expression on fresh or cryopreserved HUVEC,and the effects of IFN-γ treatment on HLA antigen expression in both groups were determined by using flow cytometry.Results No difference in SI was observed between fresh prepared and cryopreserved HUVEC(1.716±0.181 vs 1.686±0.145,P>0.05).The percentage of HLA-ABC expression was(96.6±1.9)%and(96.0±1.4)%in fresh and cryopreserved HUVEC(P>0.05),and the mean intensity for HLA-ABC expression was 84.1±5.7 and 82.4±4.8 in fresh and cryopreserved HUVEC(P>0.05),respectively.However,no HLA-DR expression was observed in both groups.When treated with IFN-γ,HLA-ABC expression was significantly up-regulated,and HLA-DR expression was induced in a dose-dependent manner.No significant difference was found in the HLA-ABC expression between fresh and cryopreserved HUVEC(P>0.05),while the HLA-DR expression in cryopreserved HUVEC was remarkably lower than in fresh HUVEC with the increase of IFN-γ(P<0.01).Conclusion The immunogenicity of HUVEC remains stable by cryopreservation without IFN-γtreatment or treated with low concentration of IFN-γ(≤50 U/ml).However,the HLA-DR expression in HUVEC was remarkably reduced in eryopreserved cells treated with a high concentration of IFN-γ(≥100 U/ml).These data indieated that the effects of cryopreservation on immunogenicity of HUVEC may result from the decreased responses of HLA-DR expression by the stimulation of IFN-γ treatment.