IL-15 mRNA expression in various T cell populations, as examined by RPA. (A) IL-15 RNA from T cells from PB of a normal individual before (lane 1) and after (lane 2) activation (PHA at 1 μg/ml and PMA at 20 ng/ml for 4 h). Lanes 3–9 contain RNA from the T cells of seven HTLV-I-infected patients with ATL. (B) Comparison of the IL-15 mRNA level between HTLV-I-positive (lanes 9–12) and -negative T cell lines (lanes 1–8). Lanes 1 and 2 contain the Jurkat T cell line at a resting state (lane 1) and an activated state (lane 2) (PHA at 1 μg/ml and PMA at 20 ng/ml for 4 h). Lanes 3–8 include the HTLV-I-non-expressing T cell lines CEM, A301, 8402T, Kit225-K6, Kit225-IG3, and Hut78, respectively. Lanes 9–12 contain HTLV-I-expressing T cell lines in the order HuT102, MT-1, MT-2, and MJ.