Th17 cells in multiple sclerosis express higher levels of JAK2, which increases their surface expression of IFN-γR2

IFN-β inhibits the expansion of Th17 cells in active multiple sclerosis (AMS), and this might contribute to improve the clinical symptoms. The effectiveness of this inhibition, however, requires intact IFN-γ signaling in T cells. In this study, we report that both mRNA and cell surface expression of the signaling chain of the IFN-γ receptor (IFN-γR2) and its cognate tyrosine kinase JAK2 are enhanced in peripheral blood Th17 cells and clones from patients with AMS compared with those with inactive multiple sclerosis (IMS) or healthy subjects (HS). IFN-γ decreased the frequency of Th17 peripheral cells and proliferation of Th17 clones from AMS patients. Stimulation of PBMCs from HS in Th17-polarizing conditions resulted in the enhancement of JAK2 expression and accumulation of cell surface IFN-γR2. The role of JAK2 in the modulation of IFN-γR2 was demonstrated as its transduction prevented rapid internalization and degradation of IFN-γR2 in JAK2-deficient γ2A cells. In conclusion, these data identify JAK2 as a critical factor that stabilizes IFN-γR2 surface expression in Th17 cells from AMS patients, making them sensitive to IFN-γ. These data may have clinical implications for a better use of IFNs in multiple sclerosis and possibly other inflammatory diseases.

Nematode Infection Enhances Survival of Activated T Cells by Modulating Accessory Cell Function

The type of immune response generated following exposure to Ag depends on a variety of factors, including the nature of the Ag, the type of adjuvant used, the site of antigenic entry, and the immune status of the host. We have previously shown that infection of rodents with Nippostrongylus brasiliensis (Nb) shifts the development of type 1 allo-specific responses toward type 2 immunity, suggesting nematode modulation of T cell activation. In this report we explore the immunomodulatory effects of Nb on T cell activation. We found that spleen cells from Nb-infected mice exhibited dramatically increased proliferation in response to Con A and anti-CD3. This hyperproliferation could be transferred in vitro to naive splenocytes by coculture with mitomycin C-treated cells from Nb-infected animals. The transfer was mediated by non-T accessory cells and supernatants derived from Con A-activated non-T cells, suggesting the involvement of a soluble factor secreted by accessory cells. The accessory cells secreted high levels of IL-6, and anti-IL-6 treatment abrogated the supernatant-induced hyperproliferation, thus confirming that IL-6 was mediating the effect. Further, spleen cells from Nb-infected mice were more resistant to activation-induced cell death (AICD) following mitogenic stimulation. Reduced AICD was also transferable and IL-6 dependent. Thus, the hyperproliferation was in part due to enhanced activated T cell survival. These phenomena mediated by accessory cells may contribute to the powerful polyclonal activation of type 2 immunity caused by nematode infection.

Nitric Oxide Suppresses Human T Lymphocyte Proliferation Through IFN-γ-Dependent and IFN-γ-Independent Induction of Apoptosis

Human normal and malignant T cells cease to proliferate, down-modulate Bcl-2 expression, and undergo apoptosis when cultured in the presence of NO-donor compounds (sodium nitroprusside and NOC12) for 48 h. At 72 h, cells that evade apoptosis start to proliferate again, overexpress both chains of the IFN-γR, and thus become susceptible to apoptosis in the presence of IFN-γ. By contrast, in the presence of IFN-γ, no apoptosis, but an increase of proliferation was displayed by control cultures of T cells not exposed to NO and not overexpressing IFN-γR chains. The NO-induced cell surface overexpression of IFN-γR chains did not affect the transduction of IFN-γ-mediated signals, as shown by the expression of the transcription factor IFN regulatory factor 1 (IRF-1). However, transduction of these signals was quantitatively modified, because IFN-γ induces enhanced levels of caspase-1 effector death in NO-treated cells. These findings identify NO as one of the environmental factors that critically govern the response of T cells to IFN-γ. By inducing the overexpression of IFN-γR chains, NO decides whether IFN-γ promotes cell proliferation or the induction of apoptosis.

A Selective Defect of IFN-γ- But Not of IFN-α-Induced JAK/STAT Pathway in a Subset of U937 Clones Prevents the Antiretroviral Effect of IFN-γ Against HIV-1

IFN-γ induces transcription of several IFN-stimulated genes (ISGs). Recently, the IFN-γ-dependent Janus kinase (JAK)/STAT pathway has been shown to mediate the activation of some ISGs, by the sequential phosphorylation of two JAK kinases (JAK1 and JAK2) and of STAT1. Given that the JAK/STAT is the major, but not the only pathway linked to the IFN-γR, aim of our work was to investigate the signal-transduction pathway(s) by which IFN-γ exerts its effects on acute replication of HIV in monocytic cells. To this end, we utilized clones previously derived from the U937 promonocytic cell line, differing for their efficient (plus clones) or inefficient (minus clones) abilities of supporting HIV replication. Unlike IFN-α, IFN-γ did not inhibit HIV replication in plus clones, whereas virus production in minus cells was efficiently inhibited by both types of IFN. Plus clones generated a JAK/STAT signal-transduction pathway in response to IFN-α, but not IFN-γ. In contrast, minus clones responded to either cytokines. The functional defect of plus clones in response to IFN-γ was correlated to a selective defect of IFN-γR2, but not IFN-γR1, membrane expression. Surprisingly enough, IFN-γ stimulation of plus clones induced IFN-stimulated gene factor 3 (ISGF3γ). These results strongly support the hypothesis that the JAK/STAT pathway is responsible for the antiretroviral effect of IFN-γ, and further provide evidence for a potential second pathway triggered by IFN-γ in the absence of IFN-γR2 chain cell surface expression and involving ISGF3γ.