Inhibition of cell growth and induction of apoptosis in K562 cells by human β₂m. (A) The proliferation of K562 cells (1 × 10⁵ cells/mL) was suppressed in the presence of more than 10 μg/mL of β₂m for 48 hours, and (B) apoptosis was induced. (C and D) The percentage of apoptotic cells was determined microscopically by counting 200 cells on in situ-stained slides. (C) Control K562 cells cultured without β₂m or (D) with 10 μg/mL of β₂m at 37°C for 48 hours. Apoptotic cells were detected using in situ staining with Apop Tag PLUS (Oncor), which gives a dark contrast to the insoluble precipitate, indicative of genomic fragmentation, as described. Arrows indicate apoptotic cells (original magnification × 200). (E) The proliferation of K562 cells was suppressed, and after more than 48 hours of incubation with 10 μg/mL of β₂m apoptosis was induced (F). Results are expressed as the mean ± SE of 3 independent experiments. Standard deviations are shown by horizontal bars.P values of less than .05 are shown as (*) and less than .01 as (**).