Surface features of human natural killer cells and antibody-dependent cytotoxic cells.

Abstract

The purpose of the present study was to examine the surface features of purified large granular lymphocytes (LGLs) (natural killer (NK) cells, antibody-dependent cytotoxic lymphoid (ADCL) cells, K-cells, Fc gamma (+) third population (non-T, non-B) lymphoid cells, T gamma cells) by scanning electron microscopy (SEM) and to compare their surface features with granulocytes, monocytes and Fc gamma (-) lymphoid cells that were all fixed for SEM under identical conditions. We have determined that 72-80% of LGLs enriched by rosette formation with sensitized erythrocytes or using Percoll gradients, have a complex microvillous surface (CMS) pattern identical to that of lymphocytes. The LGL fraction appears by SEM to represent a morphologically homogeneous population of cells. Monocytes prepared for SEM under identical conditions had distinct surface folds and granulocytes displayed numerous broad-based ridge-like profiles. The majority of lymphoid cells in an unfractioned population have a CMS pattern when incubated at room temperature (25 degrees C) before fixation, and a sparse microvillous surface (SMS) pattern when incubated at body temperature (37 degrees C). Ficoll-Hypaque (FH) also had a direct effect on the cell surface pattern. Over half of the unfractionated lymphoid cells displayed a CMS pattern after cells were washed free of FH and incubated at 37 degrees C before fixation. The CMS pattern is therefore not unique to LGLs but can be produced by the surface alteration of non-LGLs found in unfractionated buffy coat and mononuclear fractions. The interactions between LGLs and sensitized erythrocytes in an antibody-dependent cytotoxic assay system, and LGLs and K562 target cells in an NK assay system, were also examined. This is the first report that describes the surface features of human LGLs interacting with K562 target cells in an NK assay system. The LGL populations studied by SEM were determined to have a high percentage of Leu-11(+) and Leu-7(+) cells. These same population were also shown to have high antibody-dependent cytotoxicity and NK activity using the 51Cr release assay.