Natural cytotoxic reactivity of human lymphocyte subpopulations

The spontaneous cytotoxicity of human peripheral blood lymphocyte preparations from normal donors for K562 target cells was examined. Effector cells were separated into SRBC rosette forming cell (RFC) and non-rosette forming cell (non-RFC) fractions using optimal and suboptimal rosetting procedures. RFC and non-RFC fractions both had high cytotoxic activity irrespective of the rosetting procedure. Owing to the larger size of the RFC fraction, it contained a higher proportion of the total activity in the preparation. Nylon fibre column adherent and non-adherent fractions also both produced cytotoxicity. Nylon fibre non-adherent cells separated by SRBC separation gave a RFC fraction with low activity and a non-RFC fraction with high activity. Separation of nylon fibre adherent cells gave RFC and non-RFC fractions with high cytotoxic activity. Therefore cytotoxic cells did not form a discrete subpopulation and either occur in several lymphocyte subsets or show a variable capacity to form SRBC rosettes and adhere to nylon fibre.