Antibody dependent cellular cytotoxicity and mitogen responsiveness of human peripheral blood lymphocytes differing in avidity for sheep erythrocytes.

To characterize the effector cells (K-cells) in antibody-dependent cellular cytotoxicity (ADCC) against a nucleated target cell (El 4), human peripheral blood lymphocytes (PBL) were fractionated by rosette sedimentation into subpopulations differing in avidity for sheep erythrocytes (E). The fractions obtained were assayed for surface markers, and as a functional T cell marker, for responsiveness to the mitogen leucoagglutinin (La). By depleting PBL of E-receptor-bearing cells (Et+), approximately half of the cytotoxic potential was found in the Et-depleted fraction. While the Et+ fraction had low activity on a per cell basis, it nevertheless contained a significant proportion of the original cytotoxicity. By sequential E-rosetting, fractions binding E with high avidity (Et+), low avidity (Et+) or not at all (E-) were obtained. Both E-binding fractions consisted primarily of T-cells, as judged from their surface marker profiles. Both fractions responded well to La, but with different dose optima. The E- fraction contained primarily B-and null cells and did not respond to La. Significant K-cell activity was found in all these fractions. The results show that a significant fraction of the K-cells have receptors for E and these can be of either high or low avidity. Since both EH+ and EL+ fractions respond well to La and contain K-cells, a T-cell origin of the latter is suggested. However, whether or not cytotoxicity and La-responsiveness are functions of the same cells remains to be established.