Characterization of HNK-1⁺ (Leu-7) human lymphocytes. I. Two distinct phenotypes of human NK cells with different cytotoxic capability

Human lymphocytes with NK and K cell activities can be identified by the HNK-1 (Leu-7) monoclonal antibody. In these experiments, subsets of HNK-1⁺ cells from blood and bone marrow were distinguished by their expression of other cell surface antigens, their morphology, and their NK functional capability. Two-color immunofluorescence analysis revealed that subpopulations of HNK-1⁺ cells in blood expressed antigens found on mature T cells (e.g., T1, T3, T4, T8), but none expressed antigens characteristic of immature T cells (T6, T9). The majority of HNK-1⁺ cells (>60%) also expressed a myeloid antigen (M1), whereas a minority (<25%) expressed HLA-DR. HNK-1⁺ cells were separated into T3^- and T3⁺ subsets with the fluorescence-activated cell sorter and analyzed for their morphology and NK cell function. HNK⁺T3^- cells exhibited a high level of NK activity against K562 target cells and contained many cytoplasmic granules. On the other hand, HNK⁺T3⁺ cells had low NK activity and a paucity of cytoplasmic granules. The cell sizes of HNK⁺T3^- and HNK⁺T3⁺ cells were indistinguishable by light-scatter analysis. When these cell fractions were analyzed further, a reciprocal relationship between T3 and M1 antigen expression was observed. These results thus delineate two distinct subsets of human HNK-1⁺ cells in blood with different cytotoxic capability: HNK⁺T3^-M1⁺ and HNK⁺T3⁺M1^- cells. Analysis of bone marrow cells demonstrated that only 0.7% of the nucleated cells expressed the HNK-1 antigen; virtually all of these cells expressed both the T3 and T8 antigens but lacked the M1 antigen. Thus, a majority of HNK-1⁺ cell population in blood were T3^-M1⁺, whereas almost all bone marrow HNK-1⁺ cells were T3⁺M1^-. We propose that these subsets of cells represent different stages in NK cell differentiation.