Characterization of mononuclear effector cells in human blood.

The effector cells responsible for cytotoxic activity induced by phytohaemagglutinin, (PHA) pokeweed mitogen (PWM) target cells complexes with IgG antibody has been investigated using cell separation techniques based on rosette formation and separation through Hypaque-Ficoll mixtures. It was shown the PHA-induced cytotoxicity is predominantly a function of T cells and that Fc receptor-bearing cells are not involved to any major extent. Antibody-dependent killing is conversely a function of Fc receptor-bearing cells among which two subtypes can be distinguished. One of these has receptors for activated complement while the other bears Fc receptors only and has no detectable receptors for complement. PWM appears to induce cytotoxicity in both T- and non-T-cell populations but the major cell type involved appears to be Fc receptor-bearing cells similar to those mediating antibody-dependent killing. It is concluded that PHA and antibody-dependent killing are the two most useful assays for discriminating between the cytotoxic activity of T and non-T cell in clinical studies.