[Induction of nonspecific killer cell activity from human thymocyte]

Human thymocytes were fractionated to a low or high specific gravity fraction (LF or HF) by the BSA incontinuous density gradient method, and stimulated by lectin, lymphokine and mixed lymphocyte culture (MLC) in order to induce natural killer (NK)-like nonspecific killer (activated lymphocyte killer, ALK) cell activity. The results are summarized below. Thymocytes of LF induced a higher amount of interleukin 2 (IL2) by PHA stimulation than those of HF. Although PHA induced ALK activity from thymocytes of LF but not from thymocytes of HF, crude IL2 induced ALK activity from both fractions. The ALK activity induced by PHA or IL2 was abrogated by treatment of OKT3 and complement but not by OKT4 or OKT8 and complement. ALK activity and allospecific cytotoxic killer cell (allo-CTL) activity were induced from thymocytes of LF by MLC and from both fractions by MLC with IL2, but there were some differences between these two activities. Hydrocortisone suppressed the induction of ALK activity but not of allo-CTL activity. Interferon-gamma enhanced the induction of ALK activity but not of allo-CTL activity. Treatment of OKT8 and complement abrogated the ALK activity but not the allo-CTL activity. There were negligible thymocytes with NK cell markers (OKMI, Leu7, Leu11) and there was no increase of these markers or large granular lymphocytes after the induction of ALK activity. These results suggest that IL2 might be essential to induce ALK activity from human thymocytes and that this killer cell might be different from NK cells and allo-CTL.