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 lymphotropic 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 significance in the leukemogenesis of adult T cell leukemia (ATL). CD21 induction was detected at very low levels in T cell lines (Jurkat and CEM cells), and in non- or low-Tax-producing HTLV-I-infected T cell lines (Oh13T, S1T, and Su9T01 cells). In contrast, marked induction of CD21 was detected in high-Tax-producing HTLV-I-infected T cell lines (K3T, F6T, and MT-2). A Jurkat T cell clone stably transfected with tax-expressing cDNA expressed a significant amount of CD21 on the cell surface. These results strongly suggest that HTLV-I 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 EBV infection may be associated with the leukemogenesis of ATL, at least in part. However, no genome of EBV was detected in the genomic DNA of six HTLV-I-infected T cell lines or the primary ATL cells separated from all patients, indicating the irrelevance of EBV infection to ATL leukemogenesis.