Studies of the specificity of target cell lysis by cytolytic T lymphocytes (CTL) are usually based on assays measuring the competitive inhibition of radioactively labeled target cell lysis with intact unlabeled cells carrying antigens of the same or different specificities. So far, attempts to inhibit lysis with subcellular antigen preparations have met with little success. In order to obtain more favorable conditions for competitive inhibition of target cell lysis with subcellular antigens, we have introduced two modifications of the techniques of CTL induction and lysis, including a) generation of CTL by stimulating spleen cells from alloimmune mice with particulate alloantigen preparations in vitro, and b) restriction of effector to target cell interaction (in the presence or absence of particulate antigen) to 15 min, thus restricting lysis to those target cells initially bound to CTL. With these modifications of the standard 51Cr-release assay, specific inhibition by unlabeled target cells was readily and consistently demonstrable. Subcellualr particulate antigen preparations were also able to inhibit specifically CTL activity, but the inhibition was usually less marked than with intact target cells, and not every antigen preparation had the capacity to inhibit in an immunologically specific way.

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