Splenic T-killer cells can be generated by allogeneic thymic cells in conjunction with assisting factor

Abstract

CELL-MEDIATED lympholysis (CML) is known to be brought about by thymus-derived (T) killer cells that have acquired reactivity towards antigens borne on target cells. To generate such T killer cells, cooperation between two subsets of T cells within the effector population is required—namely, T helper and T pre-killer cells^1–3. Helper T cells are thought to recognise Ia antigens^4,5 and/or unique H–2 antigens⁶, while T pre-killer cells are known to recognise H–2 antigens^4,5. Ia antigens are found on B cells as well as on a certain sub-population of T cells⁷, whereas H–2 antigens have been described on virtually all B and T cells⁷. Plate has shown that a soluble factor from alloantigen-activated T helper cells assisted T pre-killer cells to differentiate into killer cells⁸. In this instance, soluble helper factor was generated in separate cultures containing mixtures of allogeneic cells, which was then assayed in a CML system from which T helper cells had been serologically removed. Since most thymic cells are known to lack Ia antigens⁷, they are conceded to be poor stimulators in both CML and mixed lymphocyte reactions^5,9–11. Nevertheless, they possess H–2 antigens and we reasoned that they might still serve to stimulate the generation of killer cells provided an assisting factor was incorporated from an exogenous source. In this way, T killer cells might be generated without at all disturbing the effector cell population by serological deletions. The data presented here support the idea that thymocytes alone are incapable of activating T helper cells, but that in the presence of exogenously produced assisting factor they do trigger development of T killer cells. The data also indicate a simple way by which assisting factors may be studied and by which requirements for CML may be delineated.