Frequency and surface phenotype of human T lymphocytes producing interleukin 2. Analysis by limiting dilution and cell cloning.

In this study we have determined the frequency and distribution of interleukin 2 (IL2)-producing cells and their precursors (IL2-P) in the two major subsets of human T cells. The two subsets were identified on the basis of their reactivity (or lack thereof) with anti-T4 or anti-T8 monoclonal antibodies. T4+T8- and T4-T8+ cells were first isolated from peripheral blood T cell populations by positive or negative selection using the fluorescence-activated cell sorter, and then analyzed for total IL2-P and cytolytic T lymphocyte precursor (CTL-P) frequencies using a limiting dilution microculture system which allows clonal growth of every T cell. The results indicated that 50-60% of peripheral blood T cells consisted of IL2-P. In the T4+T8- subset (which represents 60-65% of all T cells) about 75% of the cells were IL2-P, whereas about 15% of T4-T8+ cells exhibited this functional potential. In contrast, about 3% and greater than 95% of T4+T8- and T4-T8+ cells, respectively, were CTL-P. Thus, these data provide direct evidence that there is no absolute correlation between the surface phenotype and the functional potential of human peripheral blood T cells. Moreover, it is evident from this frequency analysis that a significant proportion of T4-T8+ cells have a dual functional potential. IL2-P and CTL-P frequencies were also determined in T cell populations which had been activated in allogeneic mixed lymphocyte culture. The IL2-P frequencies in total T, T4+T8- and T4-T8+ MLC populations were 30, 45 and 10%, respectively. Comparative analysis of IL2 production and CTL activity at the clonal level confirmed that up to 20% of alloreactive CTL with the T4-T8+ surface phenotype were able to produce IL2 upon specific stimulation. This dual functional capacity was also observed among T4+T8- CTL.