Studies of human natural killer cells. II. Analysis at the single cell level.

This report deals with the nature of conjugate-forming and lytic conjugate-forming lymphocytes, their relationship to natural killer (NK) cells, and the use of the lytic conjugate-forming cell (LCFC) assay with K562 as a measure of NK frequency in normal donors and cancer patients. Conjugate-forming cells (CFC) from granulocyte-and monocyte-depleied peripheral blood were found to be a heterogeneous population of lymphocytes that included cells forming E rosettes (T cells), EA rosettes (Fc receptor-positive cells), and cells positive for OKT3, OKT4, Mac-1, OKM1, and HNK-1. Very few surface immunoglobulin-positive cells were CFC. The CFC population was twofold to threefold enriched in cells positive for the monocyte/null cell markers OKM1 and Mac-1 and the NK cell marker HNK-1. Analysis of the LCFC showed a highly significant correlation between NK cytotoxicity and LCFC frequency, leading to the conclusion that LCFC are indeed NK cells, and that the frequency of LCFC vs. K562 is an accurate measure of NK cell frequency. Comparison of NK frequency vs. overall cytotoxicity of a group of well-defined normal donors indicated that the characteristic level of NK activity seen for different individuals was primarily due to differences in NK frequency. Two examples of abnormal NK function in patients were used to illustrate the potential of the technique. Both patients had markedly reduced cytotoxicity per effector cell, one with a comparatively high NK frequency in association with T gamma proliferation, and the other, a patient on immunosuppressive drugs, with a normal NK frequency. The combination of assays to measure NK frequency and overall NK cytotoxic activity will permit a better understanding of NK function in vivo.