Natural and antibody-dependent killer cells in the thymus.

Thymocytes contain a small population of light (o = 1.067), large cells with high cytolytic potential against natural killer target as well as against IgG- or IgM-coated erythrocytes and nucleated cells, thus displaying natural killer and antibody-dependent cellular cytotoxicity functions, but not exhibiting T killer cell capacity. As far as characterized, the cells show T cell characteristics: they are nonadherent, nonphagocytic, surface immunoglobulin-negative, C3 receptor-negative, partly Fc gamma receptor-positive, carry the receptor for Helix pomatia A agglutinin, and are, at least partly, cortisone-resistant and Thy-1-positive. The implications of this finding with respect to the lineage of natural killer and killer cells and their interdependence will be discussed briefly.