HUMAN-T-LYMPHOTROPIC-VIRUS-TYPE-I TAX INDUCTION OF CD21 EPSTEIN-BARR VIRUS RECEPTOR EXPRESSION ON T-CELLS AND ITS SIGNIFICANCE IN LEUKEMOGENESIS OF ADULT T-CELL LEUKEMIA/

CD21, which is expressed on B cells, is also expressed on human T lymp hotropic virus-type I (HTLV-I)-infected T cell lines. CD21 also serves as a receptor of Epstein-Barr virus (EBV). We evaluated the mechanism of CD21 induction on HTLV-I-infected T cells and its clinical signifi cance in the leukemogenesis of adult T cell leukemia (ATL). CD21 induc tion was detected at very low levels in T cell lines (Jurkat and CEM c ells), and in non-or low-Tax-producing HTLVI-infected T cell lines (Oh 13T, S1T, and Su9TO1 cells). In contrast, marked induction of CD21 was detected in high-Tax-producing HTLV-1-infected T cell lines (K3T, F6T , and MT-2). A Jurkat T cell clone stably transfected with tax-express ing cDNA expressed a significant amount of CD21 on the cell surface. T hese results strongly suggest that HTLV-1 Tax induces CD21 on T cells. On two-color analysis, CD21 expression was detected in CD4(+) T cells of the primary ATL cells from a subset of patients, suggesting that E BV infection may be associated with the leukemogenesis of ATL, at leas t in part. However, no genome of EBV was detected in the genomic DNA o f six HTLV-1-infected T cell lines or the primary ATL cells separated from all patients, indicating the irrelevance of EBV infection to ATL leukemogenesis.