AIM: To explore the correlation between the expressions of HLA gene and its related gene, and expression of class II transactivator (CIITA) gene induced by IFN-gamma in human ovarian cells. METHODS: The expression of HLA molecule in the tumor cells was detected by Western blot, immunohistochemical staining and flow cytometry. The expressions of transporters associated with antigen processing (TAP), low molecular weight peptides (LMP), and CIITA genes were analyzed by RT-PCR. RESULTS: Abnormal expression rate of HLA class I molecule reached 45% in the 11 ovarian cancer cells. The expressed abnormalities of HLA class I molecule had relation to those of 4 genes (TAP1, TAP2, LMP2 and LMP7). Expression of HLA class II molecule was identical with that of CIITA gene in the ovarian cancer cells or other tumor cells. After IFN-gamma treatment, expressions of HLA class I and II molecule were increased in the cells of CIITA-expressing constitutively or inducibly, while no enhancement of HLA molecule expression manifested itself in the tumor cells of that CIITA was not yet expressed after IFN-gamma induction. CONCLUSION: Deletion of TAP and LMP gene expression in the ovarian cancer cells is an important factor causing abnormal expression of HLA class I molecule, suggesting that the CIITA gene has involved in the modulation of HLA classes I and II molecule expressions in the tumor cells.