The nature of the K cell and the role of antibody-dependent cell mediated cytotoxicity (ADCC) in the rejection of tumours.

Antibody dependent lymphocytotoxicity has been characterized in cytolytic, cytostatic and microcytotoxicity assay. A " null " K cell was found in all assays and has been identified as a non phagocytic, non adherent, intermediate sized cell of lymphoid-like morphology with Mg++-independent C' receptors, lacking both T and B lymphocyte membrane antigens. In addition, recent reports suggest that a subpopulation of T cells is active in both cytolytic and microcytotoxicity assays, acting through an IgM mediating molecule. Cytolysis of tumours in a 51Cr-release assay has been demonstrated with both heterologous and allogenic antisera with varying sensitivity depending on certain membrane characteristics of different tumour lines. Cytolysis of tumours coated with syngeneic tumour specific antiserum was not demonstrated despite the presence of an equivalent amount of antibody on the tumour membrane. However, K-cell mediated cytostasis measured by the inhibition of incorporation of 125I-IUdR can be demonstrated with heterologous, allogeneic and syngeneic antisera.