Quantitative representation of all T cells committed to develop into cytotoxic effector cells and/or interleukin 2 activity-producing helper cells within murine T lymphocyte subsets.

A limiting dilution culture system based on stimulation with concanavalin A (Con A) has been used to study the quantitative distribution of helper and of cytotoxic precursor cells in Lyt-2-defined subpopulations of murine T cells. Virtually all of the selected Lyt-2+ and Lyt-2-T cells grow and expand to large clonal colonies within an 8-9-day culture period. Our data show that upon stimulation with Con A, 90% of the Lyt-2-T cells were capable to produce interleukin 2 (IL 2) activity. In addition, IL 2 activity is produced by 8-10% of Lyt-2+ T cells. However, at the clonal level, the average of the IL2 activity produced by Lyt-2+ T cells is about 8-fold less as compared to Lyt-2-T cells. Precursors of cytotoxic T cells were almost exclusively found in the Lyt-2+ population, of which about 70% displayed lytic activity in a lectin-dependent cytolysis test. For the vast majority of clones analyzed the capacity to produce IL 2 activity and the capacity to express lytic activity, was found to be mutually exclusive. A minority of clones (less than 3%) was found to simultaneously produce IL 2 activity and to express cytotoxicity. These latter cells are therefore considered as bifunctional T cells.