Interleukin-2-dependent but not independent T-cell lines infected with human T-cell leukemia virus type 1 selectively express CD45RO, a marker for persistent infection in vivo

Human T-cell leukemia virus type 1 (HTLV-1) is an etiologic agent of adult T-cell leukemia. HTLV-1 is exclusively detected in CD45RO+ T-cells in infec ted individuals, but CD45RO is weakly expressed in HTLV-1-transformed T-cel l lines in vitro. The aim of this study was to investigate the role of CD45 RO in the persistent HTLV-1 infection in vivo. Flow cytometry showed that o nly two out of eight interleukin(IL)-2-independent HTLV-1-transformed T-cel l lines expressed CD45RO, whereas all five IL-2-dependent ones expressed CD 45RO, and the level of expression was higher in IL-2-dependent than in IL-2 -independent cells. The high CD45RO expression in IL-2-dependent cell lines was not due to IL-2, since IL-2 had little effect on the expression of CD4 5RO in T-cell lines. Using western blotting, we showed that IL-2-dependent HTLV-1-transformed T-cell lines expressed a lower level of expression of th e viral transcriptional regulatory protein Tax than IL-2-independent ones, and that the level of expression correlated inversely with that of CD45RO. However, the expression of Tax in one HTLV-1-negative T-cell line little af fected the expression of CD45RO, suggesting that Tax at least alone does no t suppress the expression of CD45RO in HTLV-1-infected T-cell lines, and th at other viral or cellular factor(s) are probably involved in such suppress ion. Our results suggest that CD45RO+ Tax-low IL-2-dependent T-cell lines i n vitro correspond to the persistent HTLV-1-infected cells in vivo, and HTL V-1-infected cells in vivo are immortalized in IL-2-dependent manner.