Apoptosis and secondary necrosis of lymphocytes in culture

It has been reported that cultured peripheral B lymphocytes of chronic lymphocytic leukemia (B-CLL) patients show a high degree of apoptosis (programmed cell death). Till now, no data exist about the occurrence of in vitro apoptosis of normal B and T cells. We measured the amount of apoptosis and secondary necrosis (type 2 necrosis) in B-CLL lymphocytes and in normal peripheral B and T lymphocytes in culture. Observations were made on B-CLL lymphocytes and on normal B and T cells purified by immunomagnetic cell sorting. Apoptosis and secondary necrosis were measured using a recently described sensitive flow-cytometric assay, probing simultaneously for cell surface exposure of phosphatidylserine with the use of FITC-labeled annexin-V and for cell membrane integrity as demonstrated by the exclusion of propidium iodide. The degree of in vitro apoptosis and secondary necrosis of normal B cells appears to be higher than that of normal T cells, and even higher than that of B-CLL cells. The results indicate that cultured mature circulating normal B lymphocytes exhibit a higher cell death rate than normal T cells and B-CLL lymphocytes.