MODULATION OF INTERFERON-GAMMA RECEPTOR DURING HUMAN T-LYMPHOCYTE ALLOACTIVATION

Previous work has shown that neutralization of physiologically secreted interferon(IFN)-gamma or blockade of its receptor during T lymphocyte activation inhibits both proliferation and cytotoxic T lymphocyte generation, suggesting that IFN-gamma plays a crucial role in T lymphocyte induction and differentiation. In this study, the kinetics of the surface expression of the 90-kDa IFN-gamma receptor (IFN-gammaR) was followed during human mixed lymphocyte reaction (MLR) to alloantigens. IFN-gammaR mRNA is constitutively expressed on resting peripheral blood lymphocytes emerging from nylon wood column (NW-PBL) and its expression increases two- to threefold on alloactivated NW-PBL. IFN-gammaR protein is poorly expressed on the membrane of resting CD3+ cells, but up-modulates after 3-day MLR and sharply down-modulates at day 6. Both the p55 and the p75 chains of interleukin-2 receptor (IL-2R) were shown to up-modulate in parallel with IFN-gammaR, whereas they were still highly expressed at day 6. After alloactivation, EFN-gamma and IL-2 secretion starts at 24 h, peaks at day 3 and decreases just when IFN-gammaR and IL-2R begin to up-modulate. Proliferation peaks at day 6. Lastly, stimulation with distinct cell populations showed that the intensity of lymphocyte proliferation, IFN-gammaR membrane up-modulation, and IFN-gamma and IL-2 secretion are regulated in a parallel manner, thus suggesting that they are interrelated. Taken as whole these results demonstrate that increased expression of IFN-gammaR on T lymphocytes can be a critical event during their activation, and strongly support the hypothesis that IFN-gamma/IFN-gammaR interaction provides a signal for its progression.