Interleukin 2 induces both, growth and maturation of lectin reactive Lyt-2+ but not Lyt-2-precursor cells and regulates the cytolytic potential of effector cells.

This study investigated the requirements for lymphokines derived by recombinant (rec.) DNA technology for the induction of growth and maturation in highly purified lectin reactive T cell subsets. Nylon purified C57BL/6 lymph node T cells were treated with monoclonal anti-Lyt-2.2 or anti-L3T4 antibodies and fluorescence labeled (FITC) anti-immunoglobulin antibodies and were positively selected into Lyt-2+ (L3T4-) and Lyt-2- (L3T4+) lymphocyte subsets using a fluorescence-activated cell sorter. Sorted T lymphocytes, which were devoid of accessory cells were incubated either in bulk culture (2 X 10(2) - 3 X 10(4) cells/microculture) or under limiting dilution conditions (2.5-1,000 cells/well) with lectin (Concanavalin A, Leukoagglutinin) and rec. human Interleukin 2 (rec. hIL-2) and/or rec. mouse Interferon gamma (rec. mIFN-gamma). The data show that Lyt-2+ lymphocytes respond to lectin and rec. hIL-2 with growth and development of cytolytic activity in the absence of other exogenous factor(s) or accessory cells. The presence of monoclonal antibodies to the Interleukin 2 receptor during the sensitization phase ablated the induction of Con A reactive precursor cells of cytolytic lymphocytes (CTL-P) by either rec. hIL-2 or conventional IL-2 containing lymphokine sources, indicating the essential role of IL-2 during activation of Lyt-2+ T lymphocytes. In contrast, Lyt-2- lymphocytes could not be induced by lectin and rec. hIL-2 alone for proliferation and always required the presence of accessory cells for significant growth. Exogenous rec. m IFN gamma was unable to induce growth and cytolytic activity in Con A reactive Lyt-2+ cells and did not significantly effect their response to rec. hIL-2. Limiting dilution experiments revealed that 10-16% of the Lyt-2+ lymphocytes responded to Con A and rec. hIL-2 with growth (GTL-P). The frequencies of CTL-P, determined under similar conditions, were always lower compared to GTL-P. However the results suggest that the differences observed between both precursor populations is due to differential sensitivity of the detection system rather than to the recruitment of distinct T cell subsets. Furthermore, it was shown that at least 50% of lectin reactive CTL-P were induced by rec. hIL-2 to secrete IFN-gamma under optimal conditions. The finding that some of the conventional lymphokine sources were superior to rec. hIL-2 in the induction of growth and cytolytic activity suggests the existence of mediators distinct from IL-2 that regulate the expansion of CTL-P.(ABSTRACT TRUNCATED AT 400 WORDS)