β₂m induces apoptosis in other human leukemic and lymphoma cell lines. (A) Control CCRF-CEM cells were cultured without or (B) with 10 μg/mL β₂m at 37°C for 48 hours. Apoptotic cells were detected using in situ staining with Apop Tag PLUS (original magnification × 200). (C) Induction of apoptosis by β₂m in various cell lines. Nonlymphocytic cell lines (HL-60, NB4, THP-1, U937, and KG-1), B-lymphocytic cell lines (SKW, BALL, and Daudi), and T-lymphocytic cell lines (Jurkat, TALL, and CCRF-CEM) cells (1 × 10⁵ cells/mL) were cultured with 10 μg/mL of β₂m at 37°C for each or 48 hours, and TUNEL assays were performed. In the controls of U937 cells and BALL cells, apoptosis was induced in more than 5% of the cells. Therefore, they did not prove useful ([□] control; [▪] additive of β₂m). (D and E) Apoptosis in K562 cells (D) and in CCRF-CEM cells (E) was induced by recombinant human β₂m in the same way as with urine-derived human β₂m.