Lymphocytes that have been purified by Ficoll-Hypaque centrifugation lose antibody-dependent and natural cytotoxic activities upon culture in tissue culture medium supplemented with human plasma. However, stimulation of peripheral lymphocytes in the mixed leukocyte culture (MLC) appears to enhance killer (K) and natural killer (NK) activities in addition to generating cytotoxic T lymphocytes.
Enhancement of NK and antibody dependent activities appears to correlate with cell division as measured by 3H-thymidine uptake. However, elimination of dividing cells in the MLC by addition of 5-bromodeoxyuridine has no effect on NK and K cell activities. Since this treatment abolishes cell-mediated lympholysis mediated by cytotoxic T lymphocytes, it is a useful probe for determining the relative activities of NK, K, and cytotoxic T lymphocyte effector cells after lymphocyte stimulation.