Objective To investigate the significance of human cyomeg Movirus(HCMV)pp65 IgG antibody avidity index(AI)for the clinical diagnosis of HCMV primary infection through the experimental model of HCMV primaly infection in BALB/c mice.Methods 6～8 weeks,female,specific-pathogen-free BALB/c mice were divided into 5 groups.6 mice in each group. And he mice were injected with 2×106 PFU/m1,2×105 PFU/mi,2×104 PFU/ml,2×103 PFU/ml and 2×102 PFU/ml of HCMV intraperitoneally respectively. Another 6 mice were injected intraperitoneally with the maximum dose of HCMV kept at 56℃ for 30 min as inactivated virus group.And HF negative control group was established at same time. All the mice ere sacrificed to obtain brain and lung tissues for the following experiments after 1 montll.(1)Tissue samples obtained from mice were inoculated in human embryo fibroblasts(HF)monolayers after routine treatment for virus isolation.HCMV specific eytopathie effect(CPE) was observed bv inverted phase-contrast microscopy.HCMV UL83 DNA in the ultures as tested by PCR and pp65 antigen was detected by indirect immunofluorescence.(2)Extracted mRNA from tissue samples and HCMV pp67 mRNA were analyzed by reverse transcriptase PCR(RT-PcR).(3)Immunoglobulin M(IgM)antibody and immunoglobulin G(1gG)antibody avidity Was investigated for their usefulness in distinguishing primary genital HCMV infections rom nonprimary infections with ELISA kit using truncated pp65 protein.ResultsHCMV can be isolated in the tissues from the mice injected with 2×106 PFU/ml and 2×105 PFU/m1.RT- PCR and ELISA showed positive results in the same groups.The infective rates were 100%.The analysis of the low doses groups,inactivated group and HF negative ontrol group all showed negative results.Conclusions BALB/c mice can be infected with HCMV and appeared as primary infection after1 month.Determination of HCMV pp65 IgM and HCMV p065 IgG-AI by ELISA incorporated with virus isolation and RT-PCR are helpful for distinguishing primary infections from nonpfimary infections.The detection of HCMV p65 IgM and HCMV pp65 IgG-AI by ELISA utilizing recombinant protein pp5 as antigens can be used for preliminary screening.