Selective up‐regulation by interferon‐γ of surface molecules of the Ly‐6 complex in resting T cells: the Ly‐6A/E and TAP antigens are preferentially enhanced

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Abstract
Surface molecules encoded by the murine Ly-6 locus can transduce triggering signals in T cells and thus may play important roles in T cell function. Previously, we found that Ly-6 molecules are up-regulated by interferon (IFN)-α/β in resting T cells. Here, we examined the possible influence of IFN-γ on these molecules. Purified T cells from C57BL/6 (Ly-6.2) and BALB/c (Ly-6.1) mice were incubated in vitro with recombinant murine IFN-γ and the expression of Ly-6 antigens was measured by flow cyto-fluorometry. It was found that both Ly-6A/E and T cell-activating protein (TAP) molecules are markedly enhanced while Ly-6C is less affected. Under the same conditions, other T cell surface molecules showed no or marginal changes. The effect of IFN-γ on Ly-6A/E and TAP expression reached a maximum with as little as 10 U/ml and required only 18–24 h of incubation. Moreover, the enhancement of Ly-6A expression induced by IFN-γ was stable for at least 5 days. Analysis of T cell subsets further revealed that IFN-γ-induced augmentation of Ly-6A (C57BL/6 mice) involves both Lyt-2+ and L3T4+ cells while the increase of Ly-6E (BALB/c mice) is more pronounced in Lyt-2+ cells. The functional consequence of these phenotypic alterations was evaluated by studying the mitogenic responses of T cells to antibody-mediated Ly-6 cross-linking in the presence of phorbol myristate acetate. Pretreatment of resting T cells with IFN-γ dramatically increased the responses to anti-Ly-6A and anti-Ly-6E monoclonal antibodies. IFN-γ treatment also boosted the stimulation induced by anti-TAP monoclonal antibody when this stimulation was performed under suboptimal conditions. Therefore, IFN-γ selectively up-regulates the Ly-6A/E and TAP activation pathways in resting T cells. We speculate that this effect may contribute to the immunoregulatory activities of IFN-γ.