Specificities in natural cell-mediated cytotoxicity by the cross-competition assay.

The cross-competition assay was applied to natural cell-mediated cytotoxicity in human, mouse and rat systems. The results showed that what appeared to be non-selective effects of natural cytotoxicity were in fact highly specific. Each effector suspension included natural effector cells (N cells) that recognized and reacted specifically with many different antigens on target cells, resulting in overall non-selectivity. The specificity of the reaction for each target cell was demonstrated by the selective inhibition of natural cytotoxicity achieved when competitor cells sharing antigens with the target cell were added. Sharing of common target antigens was demonstrated by selective cross-inhibition which was then used to investigate antigens on target cells.