In this study, the author explored the role of interferon regulatory factor 7 (IRF7) and latent membrane protein 1 (LMP1) on the regulation of antigen presenting molecules in B-lymphoblastoid cell lines. First, the author observed the endogenous expression of IRF7 and LMP1 in paired EBV-positive B-lymphoblastoid cell lines, Sav I and Sav III, which represent EBV type I and type III latency, respectively. The Sav I cell, which does not express LMP1, showed very low levels of endogenous IRF7 in the cytoplasm. However, Sav III cells, which express large amounts of LMP1, contained high levels of endogenous IRF7 in both the cytoplasm and the nucleus. The expression of surface MHC class I antigen was 7.8-fold higher in Sav III compared with Sav I cells when measured by fluorescence activated cell sorter (FACS) analysis. To understand whether IRF7 is involved in regulation of MHC I and TAP1, LMP1 or IRF7 were expressed by cotransfection in DG75 cells. Levels of TAP1 protein were up-regulated by LMP1 and IRF7 alone, and by LMP1 co expression with IRF7, the expression level was highest after co-transfection of LMP1 with IRF7. TAP1 promoter activity was also up-regulated to 2.4, 2.0, 3.2-fold by LMP1, by IRF7, and by LMP1 plus IRF7, respectively. Surface expression of MHC class I antigen was up-regulated by LMP1 alone and LMP1 plus IRF7, but not by IRF7 alone. These results suggest that IRF7 induces the expression of TAP1, but not MHC class I antigen and that LMP1 and IRF7 have additive effects on the expression of TAP1 protein.