Broad programming by IL-2 receptor signaling for extended growth to multiple cytokines and functional maturation of antigen-activated T cells.

Coincident production of IL-2 and induction of high-affinity IL-2R upon TCR engagement has precluded a clear distinction for the biological outcome of signaling through TCR/costimulatory molecules vs the IL-2R. Using a novel transgenic mouse on the IL-2Rbeta(-/-) genetic background, this study has separated the relative outcome of signaling through the TCR and IL-2R. We show that stimulation through the TCR and CD28 or CD40 ligand directly leads to T cell activation and several rounds of proliferation in an IL-2-independent fashion. However, this stimulation is insufficient for extended T cell growth to multiple cytokines or differentiation into CTL or IFN-gamma-secreting effector T cells. IL-2 is required for these functions in part by regulation of cyclin D3 and granzyme B. Somewhat less efficiently, IL-4 stimulation of these transgenic T cells redundantly rescued many of these activities. These data demonstrate a fundamental requirement for IL-2 and perhaps other common gamma-chain-dependent cytokines to promote selective gene expression by Ag-activated T cells for their subsequent growth and differentiation into effector T lymphocytes.

Normal lymphoid homeostasis and lack of lethal autoimmunity in mice containing mature T cells with severely impaired IL-2 receptors.

The importance of IL-2Rbeta function for immune regulation is highlighted by the severe impairment in lymphoid cell function in IL-2Rbeta-deficient mice. It has been speculated that failed IL-2/IL-2R signaling in peripheral T cells causes the associated autoimmunity, imbalanced peripheral lymphoid homeostasis, and defective T cell function. This study explored the requirement for IL-2Rbeta function in mature T lymphocytes. We show that transgenic thymic expression of the IL-2R beta-chain in IL-2Rbeta-deficient mice prevents lethal autoimmunity, restores normal production of B lymphocytes, and results in a peripheral T cell compartment that is responsive to triggering through the TCR, but not the IL-2R. The dysfunction of the IL-2R is illustrated by the near complete failure of mature T cells to proliferate to IL-2 in vitro and in vivo, to differentiate into CTL, and to up-regulate IL-2Ralpha expression. These data indicate that lymphoid homeostasis is largely maintained despite a nonfunctional IL-2R in mature T lymphocytes and suggest that IL-2Rbeta provides an essential signal during thymic development to regulate self-reactivity.

Regulation of B lymphocyte responses to IL-4 and IFN-gamma by activation through Ly-6A/E molecules.

The Ly-6 family of cell surface molecules has previously been shown to participate in T cell activation. We show that Ly-6A/E proteins also modulated the response of normal B lymphocytes in three separate in vitro assays. First, unfractionated or small resting B cells proliferated when cultured with IFN-gamma, IL-4, and an anti-Ly-6A/E mAb. Second, this anti-Ly-6A/E mAb restored B cell proliferation responses that were inhibited when coculturing the B cells in IFN-gamma, IL-4, and anti-IgM. Third, anti-Ly-6A/E specifically up-regulated the cell surface expression of its own Ag, and this response was dependent upon co-stimulation with IFN-gamma. Mixing of T and B cells in culture suggested that T cells did not contribute substantially to the B cell proliferative response. Moreover, up-regulation of Ly-6A/E was observed for one B cell lymphoma, WEHI-231. Therefore, it appeared that modulation of B cell function by anti-Ly-6A/E was due to a direct effect of the mAb binding to the B cells. Taken together, these data suggest Ly-6A/E proteins are functional on B cells and may play a regulatory role in B cell activation.

Tumor necrosis factor synergistically acts with IFN-gamma to regulate Ly-6A/E expression in T lymphocytes, thymocytes and bone marrow cells.

The Ly-6 alloantigens represent a family of phosphatidylinositol anchored proteins that function in the process of T lymphocyte activation and whose expression are often induced on T and B lymphocytes after activation by mitogens or Ag. Previous studies have shown that the induction of Ly-6 alloantigens in T cells is at least in part due to the action of IFN-alpha/beta or IFN-gamma. In the present report, we have demonstrated that IFN-gamma also induced Ly-6 molecules on B lymphocytes, several B cell tumors, and bone marrow cells. Furthermore, we now show that TNF also participates in the induction of at least one of the Ly-6 proteins, Ly-6A/E. TNF was found to synergize with IFN-gamma to induce Ly-6A/E expression in thymocytes, T lymphocytes, bone marrow cells, but not B lymphocytes. For T lymphocytes, the synergistic induction of Ly-6A/E by TNF was restricted to cells from the Ly-6.1 haplotype, whereas IFN-gamma was sufficient to fully induce Ly-6A/E expression in cells from the Ly-6.2 haplotype. This result is consistent with the notion that there is more complex regulation of the Ly-6A/E molecules in T cells obtained from the Ly-6.1 haplotype. For T lymphocytes from BALB/c (Ly-6.1) mice, Ly-6A/E, but not Ly-6C, molecules were synergistically induced by IFN-gamma and TNF. The induction of Ly-6A/E molecules on BALB/c T cells resulted in an enhanced capacity to activate these cells through the Ly-6 T cell activation pathway. One transformed T cell line, 5.1.2, was also identified whose Ly-6A/E molecules were synergistically induced by IFN-gamma and TNF. Optimal expression of Ly-6A/E molecules on 5.1.2 cells required continuous culture of this cell line with these two cytokines and resulted in the detection of optimal levels of cytoplasmic Ly-6A/E mRNA by Northern blot analysis. This latter result suggests that IFN-gamma and TNF regulate Ly-6A/E at the level of transcription and/or mRNA stabilization.