Cytokine dependence of V gamma 3 thymocytes: mature but not immature V gamma 3 cells require endogenous IL-2 and IL-7 to survive--evidence for cytokine redundancy.

It has previously been described that V gamma 3 cells can proliferate extensively in vitro in the presence of different cytokines. Here, the role of cytokines in the maintenance of V gamma 3 cells in the thymus has been determined. Culture of fetal thymocytes in cell suspension for 24 h showed that, whereas immature TCRlowHSAhigh V gamma 3 cells remained viable, all mature TCRhighHSAlow V gamma 3 cells died. These cells died by apoptosis since protein synthesis was required and flow cytometric analysis as well as DNA gel electrophoresis showed that the DNA was degraded to oligonucleosomal bands. Addition of IL-2, IL-4 or IL-7 to suspension cultures of fetal thymocytes rescued V gamma 3 cells from dying. Addition of IL-1, IL-3, IL-5, IL-6, IL-9, TNF-alpha or IFN-gamma was without effect. Phenotypic analysis showed that the alpha-chain of the IL-2 receptor (IL-2R alpha) was expressed by part of the immature V gamma 3 thymocytes, all mature V gamma 3 cells expressed the beta-chain of the IL-2 receptor (IL-2R beta). Addition of anti-IL-2R beta mAb to fetal thymic organ culture (FTOC) resulted in a moderate reduction of the cell number of mature V gamma 3 thymocytes. Addition of anti-IL-2R alpha, anti-IL-4 or anti-IL-7 mAb had no effect. The cell number of mature V gamma 3 cells was highly reduced when both anti-IL-2R beta and anti-IL-7 mAb were added to FTOC.(ABSTRACT TRUNCATED AT 250 WORDS)