Apoptosis of human lymphocytes in the absence or presence of internucleosomal DNA cleavage

Treatment of human peripheral blood lymphocytes with heat shock, ionising radiation, bleomycin, etoposide, or hydrogen peroxide induced morphological evidence of apoptosis that was associated with the appearance of 50 Kb double-stranded DNA fragments. The apoptotic response elicited by the above agents, with the exception of hydrogen peroxide, was also paralleled by the formation of internucleosomal DNA fragments. This effect of hydrogen peroxide, however, appeared to be confined to human lymphocytes, since apoptosis induced by the oxidant in U937 cells was in fact associated with DNA laddering