Specificity and effector-target interaction.

When effector cells were tested on a number of target cells, the most obvious effect observed was a nonselective cytotoxicity that is now known as natural cell-mediated cytotoxicity. The apparent nonselectivity was a result of specific cytotoxic activity against many different antigens on target cells. This specificity was demonstrated in the cross-competition assay in which target cells sharing common antigens selectively inhibited natural cytotoxicity.