The syngeneic T-T lymphocyte reaction (STTLR). II. Induction of primary T anti-T cell cytotoxic responses in vitro in T cell cultures stimulated with syngeneic self-reactive T cells.

In the previous paper in this series, we described a form of self-reactivity among T cells called the "syngeneic T-T lymphocyte reaction" (STTLR). The phenomenon involves responder T cells that are stimulated to proliferate by irradiated antigen or self-reactive cloned T cell lines. The proliferative STTLR occurs in cultures rigorously depleted of conventional APC and is inhibitable by anti-Ia antibodies of the appropriate specificity. We also showed that both L3T4+ Lyt2- and L3T4- Lyt2+ T cell subsets participate in the STTLR-induced by the IEk-specific Lbd T cell line. In this paper, we report our studies on the effector phase of STTLRs, in particular, the cytotoxic responses induced by Lbd cells. We demonstrate that uncloned and cloned lines (called Dbl) of anti-Lbd cytotoxic cells are L3T4- Lyt2+ effector cells that kill Lbd, antigen-reactive T cells, and syngeneic B cells stimulated with LPS. They also kill syngeneic splenic cells stimulated with Con A for 72 h or less; longer culture periods in the presence of Con A yield Dbl-resistant T cells. Resting T cells are also resistant to Dbl cells. Using LPS-induced splenic B cells from H-2 congenic mice, we map the anti-self specificity of uncloned and cloned anti-Lbd cells to the Kk + IAk regions of the MHC. Seemingly concordant results were obtained using L transformants expressing IAk molecules on their surface. However, control studies with fibroblast lines and UV-induced fibrosarcoma cells unexpectedly revealed a high susceptibility to lysis by Dbl cells among certain Ia- cell lines. These results suggested that the antigen recognized by Dbl cells is not IAk itself but either an MHC-encoded or MHC-regulated gene product expressed by activated T and B cells and certain tumor cells. The target antigen is important in immunoregulation because Dbl cells suppress both the proliferation of Lbd cells to syngeneic cells and primary T cell-dependent anti-SRC PFC responses. From an immunoregulatory viewpoint, the existence of Lbd-Dbl cells offers several appealing features. Since Lbd cells cannot activate resting B cells or replace antigen-specific helper cells, they cannot initiate immune responses nonspecifically. In the presence of the appropriate antigen-specific helper T cells, Lbd and other self-reactive cells can amplify an immune response and thus facilitate its exponential growth. Since the self-reactive cells activate the Dbl cytotoxic circuit described above, they also provide the stimulus required to terminate immune responses quickly.(ABSTRACT TRUNCATED AT 400 WORDS)