Normal human blood lymphocytes with affinity for ox red cells sensitized with IgG antibody, for normal or papain-treated sheep red cells and for ox red cells coated with mouse complement were used for rosette formation and the rosetting cells separated by density gradient centrifugation on Ficoll/Hypaque. The non-rosetting cells at the interface were collected and compared with cell suspensions before treatment for direct and antibody-dependent cytotoxicity of human target cells. Depletion of Fc-receptor-bearing lymphocytes strongly decreased antibody-dependent cell-mediated cytotoxicity; reduction in the number (or depletion) of T cells and cells with C′3 receptor had no effect, showing the same or enhanced K-cell activity. It is concluded that one type of K or killer cell has Fc receptors but lacks C′3 receptors.

The influence of carbonyl iron treatment on different human mononuclear cell subsets was investigated. There is evidence that, in addition to removal of phagocytic cells, lymphocytes are depleted, B cells being more affected than other subpopulations.

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