Hapten-specific, class II-restricted killing by cloned T cells: direct lysis and production of a cytotoxic factor.

DNP-specific, class II-restricted cloned T cells were shown to kill DNP-bearing A20.2J (A20-DNP) antigen-presenting cells. This killing was DNP-specific and was restricted by IA. Results from bystander cytotoxicity, cold-target inhibition, and protein and lymphokine inhibition experiments indicated that killing of A20-DNP targets was mediated by direct lysis. In addition to the direct lysis, antigen stimulation of the T cells also resulted in production of a soluble cytolytic factor which killed bystander L929 fibroblast cells. This killing was sensitive to inhibition of protein synthesis and lymphokine production but was not affected by the addition of cold A20-DNP target cells. Additional studies showed that other antigen-presenting cells, i.e., DNP-bearing P388D1 and splenic macrophages, were also lysed by the cloned T cells. These findings may indicate that lysis of target cells by nominal antigen-specific, class II-restricted T cells plays a role in immune regulation and/or immune protection.