Similarities between LAK cells derived from human thymocytes and peripheral blood lymphocytes: expression of the NKH-1 and CD3 antigens.

Human thymocytes are devoid of NK cells but develop lymphokine-activated killer (LAK) activity after culture with recombinant interleukin-2 (rIL-2). The most active precursor for this activity appears to be a CD3-negative cell. The purpose of these studies was to compare the phenotype and functional activities of thymocyte and peripheral blood lymphocyte (PBL) LAK cells. Following culture, rIL-2-activated thymocytes resemble PBL-generated LAk and PBL NK cells. For each of these populations, lytic activity is highest in NKH-1-positive cells. Two-color fluorescence of each population also indicates that NKH-1+ cells are highly granular, as measured by staining with the lysosomotropic vital dye quinacrine. PBL, PBL-derived LAK cells, and thymus-derived LAK cells have a portion of cells that express both CD3 and NKH-1. However, approximately 60-80% of NKH-1+ cells lack detectable CD3. This suggests that both CD3+ and CD3- cells may be capable of LAK activity. Thymic-derived LAK cells respond to interferon in a manner very similar to NK and PBL-derived LAK cells, but lack the NK-associated CD16 antigen. Thus, despite the absence of NK cells in the thymus, it is possible to generate thymocyte LAK activity which bears a strong resemblance to LAK activity derived from peripheral blood lymphocytes.