Cytokine dependence of Vγ 3 thymocytes: mature but not immature Vγ3 cells require endogenous IL-2 and IL-7 to survive— evidence for cytokine redundancy

Abstract

It has previously been described that V_γ3 cells can proliferate extensively in vitro in the presence of different cytokines. Here, the role of cytokines in the maintenance of V_γ3 cells in the thymus has been determined. Culture of fetal thymocytes in cell suspension for 24 h showed that, whereas immature TCR^lowHSA^highV_γ3 cells remained viable, all mature TCR^highHSA_lowV_γ 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_γ3 cells from dying. Addition of IL-1, IL-3, IL-5, IL-6, IL-9, TNE-α or IFN-_γ was without effect. Phenotypic analysis showed that the α-chain of the IL-2 receptor (IL-2Rα) was expressed by part of the immature V_γ3 thymocytes, all mature V_γ3 cells expressed the p-chain of the IL-2 receptor (IL-2RP). Addition of anti-IL-2Rα mAb to fetal thymic organ culture (FTOC) resulted in a moderate reduction of the cell number of mature V_γ3 thymocytes. Addition of anti-IL-2Ra, anti-IL-4 or anti-IL-7 mAb had no effect. The cell number of mature V_γ3 cells was highly reduced when both anti-IL-2Rp and anti-IL-7 mAb were added to FTOC. These results show that IL-2 and IL-7 are actively involved in the maintenance of mature V_γ3 cells in the thymus. This cytokine dependence of mature V_γthymocytes may explain their selective localization in skin epithelium.