Use of positively selected Lyt-2+ mouse splenocytes to examine interleukin-2 secretion in responses to alloantigens and to TNP-modified syngeneic cells

Current models for T-cell interactions in the generation of cytotoxic T lymphocytes have encountered a technical problem, since it has until recently been impossible to purify the peripheral Lyt-1⁺2⁺ subset from the Lyt-1⁺2^? helper cell set. Reports that the helper factor Interleukin-2 (IL-2) can be synthesized by Lyt-2⁺ spleen cells have suggested that the peripheral Lyt-2⁺ set, unlike Lyt-2⁺ thymocytes, might not depend on help from Lyt-1⁺2^? cells. To clarify this question, we have produced spleen Lyt-2⁺ cells, and the complementary Lyt-2^? set, by a positive selection method. The Lyt-2⁺ cells were able to produce high levels of anti-hapten CTL only if supplemented with either Lyt-2^? cells or with semi-purified IL-2. Although IL-2 synthesis from Lyt-2⁺ cells, or from unseparated T cells, could be induced by H-2I region-disparate stimuli, Lyt-2⁺ cells produced very little IL-2 in response to H-2I or to H-2K region-disparate cells. IL-2 synthesis in hapten-stimulated cultures was found not to depend on the presence of the hapten per se, and probably represents a response to components of the fetal calf serum supplementation. Lyt-2⁺ cells were also much less able to generate IL-2 than Lyt-2^? cells in response to these stimuli. Cell mixing experiments provided no evidence that Lyt-2⁺ cells could suppress IL-2 secretion by Lyt-2^? cells. We conclude that generation of CTL from splenic Lyt-2⁺ cells requires IL-2 produced by Lyt-2^? cells, because Lyt-2⁺ cells do not produce high levels of IL-2 themselves, even when stimulated across an H-2K difference alone.