T-cell lines which cooperate in generation of specific cytolytic activity

Abstract

THE unidirectional mixed leukocyte culture (MLC) is characterised by cell proliferation and by the development of cytolytic T lymphocytes (CTL)^1–3. In murine MLC, the generation of CTL seems to involve proliferation of at least two sub-populations of responding T cells—T cells of the Ly-2⁺3⁺ phenotype, which differentiate into CTL, and cells of the Ly-1⁺ phenotype, which seem to ‘help’ or ‘amplify’ the CTL re-sponse^4–6. The mechanism by which ‘amplifier cells’ augment the CTL response is unclear; recent reports have shown, however, that CTL precursors present in populations of long-term MLC or of immune spleen cells^7,8 can respond to supernatant fluid obtained from allogeneic MLC or mitogen-stimulated spleen cell cultures in the absence of specific antigen. Several groups using such conditioned medium have reported the successful long-term culture of normal and antigen-specific immune T cells in the absence of alloantigen stimuli^9–11. Whereas amplifier supernatant fluids seem to substitute functionally for a T-cell subpopulation (Ly-1⁺?) in the absence of alloantigen, there is only indirect evidence that amplifier cells can be activated by alloantigen to release one or several soluble factors that influence the differentiation or proliferation ofCTL^12–14. We have used modifications of techniques previously described for the long-term culture of immune T cells to isolate several cloned lines of MLC-reactive T cells, including a non-cytolytic T-cell line which, when co-cultured with alloantigen, permits another cell line to proliferate and express specific cytolytic activity.