Loss of interferon-induced Stat1 phosphorylation in activated T cells

TRAF3 enhances type I interferon receptor signaling in T cells by modulating the phosphatase PTPN22

Type I interferons (IFNs) are among the most powerful tools that host cells deploy against intracellular pathogens. Their effectiveness is due both to the rapid, directly antiviral effects of IFN-stimulated gene products and to the effects of type I IFN on responding immune cells. Type I IFN signaling through its receptor, IFNAR, is tightly regulated at multiple steps in the signaling cascade, including at the level of IFNAR downstream effectors, which include the kinase JAK1 and the transcriptional regulator STAT1. Here, we found that tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) enhanced the activation of JAK1 and STAT1 specifically in CD4+ T cells by preventing recruitment of the negative regulatory phosphatase PTPN22 to the IFNAR complex. The balance between signals through IFNAR and other cytokine receptors influences CD4+ T cell differentiation and function during infections. Our work reveals TRAF3 and PTPN22 as key regulators of CD4+ T cell activation by type I IFNs.

Visualizing the Selectivity and Dynamics of Interferon Signaling In Vivo

Interferons (IFN) are pleiotropic cytokines essential for defense against infection, but the identity and tissue distribution of IFN-responsive cells in vivo are poorly defined. In this study, we generate a mouse strain capable of reporting IFN-signaling activated by all three types of IFNs and investigate the spatio-temporal dynamics and identity of IFN-responding cells following IFN injection and influenza virus infection. Despite ubiquitous expression of IFN receptors, cellular responses to IFNs are highly heterogenous in vivo and are determined by anatomical site, cell type, cellular preference to individual IFNs, and activation status. Unexpectedly, type I and II pneumocytes, the primary target of influenza infection, exhibit striking differences in the strength and temporal dynamics of IFN signaling associated with differential susceptibility to the viral infection. Our findings suggest that time- and cell-type-dependent integration of distinct IFN signals govern the specificity and magnitude of IFN responses in vivo.

Signaling Pathways of Type I and Type III Interferons and Targeted Therapies in Systemic Lupus Erythematosus

Type I and type III interferons (IFNs) share several properties in common, including the induction of signaling pathways, the activation of gene transcripts, and immune responses, against viral infection. Recent advances in the understanding of the molecular basis of innate and adaptive immunity have led to the re-examination of the role of these IFNs in autoimmune diseases. To date, a variety of IFN-regulated genes, termed IFN signature genes, have been identified. The expressions of these genes significantly increase in systemic lupus erythematosus (SLE), highlighting the role of type I and type III IFNs in the pathogenesis of SLE. In this review, we first discussed the signaling pathways and the immunoregulatory roles of type I and type III IFNs. Next, we discussed the roles of these IFNs in the pathogenesis of autoimmune diseases, including SLE. In SLE, IFN-stimulated genes induced by IFN signaling contribute to a positive feedback loop of autoimmunity, resulting in perpetual autoimmune inflammation. Based on this, we discussed the use of several specific IFN blocking strategies using anti-IFN-α antibodies, anti-IFN-α receptor antibodies, and IFN-α-kinoid or downstream small molecules, which intervene in Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathways, in clinical trials for SLE patients. Hopefully, the development of novel regimens targeting IFN signaling pathways will shed light on promising future therapeutic applications for SLE patients.

Differential IL-7 responses in developing human thymocytes

Interleukin (IL)-7 is a factor essential for mouse and human thymopoiesis. Mouse thymocytes have altered sensitivities to IL-7 at different developmental stages. CD4/CD8 double positive (DP) mouse thymocytes are shielded from the influence of IL-7 because of loss of CD127 (IL-7Ralpha). In this study, we assessed IL-7 receptor expression and IL-7 signaling in human thymocytes. We found human DP cells to be severely limited in their ability to phosphorylate STAT-5 in response to IL-7. The relative expression levels of the IL-7-inducible proteins Bcl-2 and Mcl-1 were also lower in human DP cells, consistent with a stage-specific decrease in IL-7 responsiveness. IL-7 responses were restored in a subset of cells that matured past the DP stage. Unlike the regulation of IL-7 signaling in mouse thymocytes, loss of IL-7 signaling in human DP cells was not due to absence of CD127, but instead correlated with downregulation of CD132 (common gamma chain).

Control of T helper cell differentiation through cytokine receptor inclusion in the immunological synapse

The antigen recognition interface formed by T helper precursors (Thps) and antigen-presenting cells (APCs), called the immunological synapse (IS), includes receptors and signaling molecules necessary for Thp activation and differentiation. We have recently shown that recruitment of the interferon-gamma receptor (IFNGR) into the IS correlates with the capacity of Thps to differentiate into Th1 effector cells, an event regulated by signaling through the functionally opposing receptor to interleukin-4 (IL4R). Here, we show that, similar to IFN-gamma ligation, TCR stimuli induce the translocation of signal transducer and activator of transcription 1 (STAT1) to IFNGR1-rich regions of the membrane. Unexpectedly, STAT1 is preferentially expressed, is constitutively serine (727) phosphorylated in Thp, and is recruited to the IS and the nucleus upon TCR signaling. IL4R engagement controls this process by interfering with both STAT1 recruitment and nuclear translocation. We also show that in cells with deficient Th1 or constitutive Th2 differentiation, the IL4R is recruited to the IS. This observation suggest that the IL4R is retained outside the IS, similar to the exclusion of IFNGR from the IS during IL4R signaling. This study provides new mechanistic cues for the regulation of lineage commitment by mutual immobilization of functionally antagonistic membrane receptors.

The immunity-related GTPase Irgm1 promotes the expansion of activated CD4+ T cell populations by preventing interferon-gamma-induced cell death

Mice deficient in the interferon-gamma (IFN-gamma)-inducible, immunity-related GTPase Irgm1 have defective host resistance to a variety of intracellular pathogens. This greater susceptibility to infection is associated with impaired IFN-gamma-dependent macrophage microbicidal activity in vitro. Here we show that Irgm1 also regulated the survival of mature effector CD4(+) T lymphocytes by protecting them from IFN-gamma-induced autophagic cell death. Mice deficient in both IFN-gamma and Irgm1 were 'rescued' from the lymphocyte depletion and greater mortality that occurs in mice singly deficient in Irgm1 after mycobacterial infection. Our studies identify a feedback mechanism in the T helper type 1 response that limits the detrimental effects of IFN-gamma on effector T lymphocyte survival while promoting the antimicrobial functions of IFN-gamma.

Janus-kinase-3-dependent signals induce chromatin remodeling at the Ifng locus during T helper 1 cell differentiation

Differentiation of naive CD4+ T cells into T helper type 1 (Th1) effector cells requires both T cell receptor (TCR) signaling and cytokines such as interleukin-12 and interferon gamma (IFN-gamma). Here, we report that a third cytokine signal, mediated by the Janus family tyrosine kinase 3 (Jak3) and signal transducer and activator of transcription 5 (STAT5) pathway, is also required for Th1 cell differentiation. In the absence of Jak3-dependent signals, naive CD4+ T cells proliferate robustly but produce little IFN-gamma after Th1 cell polarization in vitro. This defect is not due to reduced activation of STAT1 or STAT4 or to impaired upregulation of the transcription factor T-bet. Instead, we find that T-bet binding to the Ifng promoter is greatly diminished in the absence of Jak3-dependent signals, correlating with a decrease in Ifng promoter accessibility and histone acetylation. These data indicate that Jak3 regulates epigenetic modification and chromatin remodeling of the Ifng locus during Th1 cell differentiation.

Disruption of thymopoiesis in ST6Gal I-deficient mice

Thymocyte development is accompanied by sequential changes in cell surface glycosylation. For example, medullary thymocytes have increased levels of alpha2,3-linked sialic acid and a loss of asialo core 1 O-glycans as compared to cortical thymocytes. Some of these changes have been linked to fine tuning of the T cell receptor avidity. We analyzed ST6Gal I transcript abundance and levels of alpha2,6-linked sialic acid across thymocyte subsets. We found that ST6Gal I transcript levels increased following T cell receptor beta-selection suggesting that this sialyltransferase may influence the development of early thymocyte populations. Indeed, low levels of alpha2,6-linked sialic acid were found in the earliest T lineage cells, and then increased in T cell receptor beta-selected cells. To determine whether ST6Gal I influences T cell development, we analyzed ST6Gal I-deficient mice for disruptions in thymocyte populations. We found reduced thymic cellularity in the ST6Gal I-deficient mice starting in the early thymocyte compartments.

Impaired thymopoiesis in interleukin-7 receptor transgenic mice is not corrected by Bcl-2

Murine thymocytes down-regulate IL-7 responsiveness following beta-selection and reacquire sensitivity after positive selection. To assess the potential consequences of IL-7 signaling during this phase of development, transgenic IL-7 receptor alpha (IL-7Ralpha) mice were evaluated for IL-7 responsiveness as gauged by STAT-5 phosphorylation. Transgenic IL-7Ralpha expression increased the percentage of thymocytes responsive to IL-7 yet resulted in a decrease in total thymic cellularity. Aberrant thymocyte development in transgenic mice was first manifested by a reduction of DN3 thymocytes that correlated with lower Bcl-2 expression. Surprisingly, transgenic restoration of Bcl-2 expression did not correct thymic hypocellularity induced by IL-7Ralpha overexpression. These findings demonstrate that failure to appropriately downregulate IL-7Ralpha expression interferes with thymocyte development past the pro-T stage resulting in significantly lower levels of mature thymocytes.

Two-Sided Roles of IL-27: Induction of Th1 Differentiation on Naive CD4+T Cells versus Suppression of Proinflammatory Cytokine Production Including IL-23-Induced IL-17 on Activated CD4+T Cells Partially Through STAT3-Dependent Mechanism

Recent lines of evidence have demonstrated that IL-27, a newly identified IL-12-related cytokine, has two apparently conflicting roles in immune responses: one as an initiator of Th1 responses and the other as an attenuator of inflammatory cytokine production. Although the IL-27-mediated Th1 initiation mechanism has been elucidated, little is known about the molecular basis for the suppression of cytokine production. In the present study, we demonstrated that IL-27 suppressed the production of various proinflammatory cytokines by fully activated CD4+ T cells while it had no effect on the cytokine production by CD4+ T cells at early phases of activation. IL-27 also suppressed IL-17 production by activated CD4+ T cells, thereby counteracting IL-23, another IL-12-related cytokine with proinflammatory effects. In fully activated CD4+ T cells, STAT3 was preferentially activated by IL-27 stimulation, whereas both STAT1 and 3 were activated by IL-27 in early activated CD4+ T cells. Lack of STAT3 in fully activated cells impaired the suppressive effects of IL-27. These data indicated that the preferential activation of STAT3 in fully activated CD4+ T cells plays an important role in the cytokine suppression by IL-27/WSX-1.

Complex Modulation of Cell Type-Specific Signaling in Response to Type I Interferons

The type I interferons (IFNs) are pleiotropic cytokines that regulate many different cellular functions. The major signaling pathway activated by type I IFNs involves sequential phosphorylation of the tyrosine residues of the Janus kinase (JAK) and signal transducers and activators of transcription (STAT) proteins, providing the primary mechanism through which gene expression is induced. Recent work has shown that the responses are quite complex, as shown by different responses to specific subtypes of type I IFN, activation of kinases in addition to JAKs, patterns of activation of all seven STATs in different cells, and activation of transcription factors other than STATs. The type I IFNs use this complexity to regulate many different biological functions in different types of cells, by activating different specific signals and patterns of gene expression.

Comprehensive gene expression profiling following DNA vaccination of rainbow trout against infectious hematopoietic necrosis virus

The DNA vaccine based on the glycoprotein gene of Infectious hematopoietic necrosis virus induces a non-specific anti-viral immune response and long-term specific immunity against IHNV. This study characterized gene expression responses associated with the early anti-viral response. Homozygous rainbow trout were injected intra-muscularly (I.M.) with vector DNA or the IHNV DNA vaccine. Gene expression in muscle tissue (I.M. site) was evaluated using a 16,008 feature salmon cDNA microarray. Eighty different genes were significantly modulated in the vector DNA group while 910 genes were modulated in the IHNV DNA vaccinate group relative to control group. Quantitative reverse-transcriptase PCR was used to examine expression of selected immune genes at the I.M. site and in other secondary tissues. In the localized response (I.M. site), the magnitudes of gene expression changes were much greater in the vaccinate group relative to the vector DNA group for the majority of genes analyzed. At secondary systemic sites (e.g. gill, kidney and spleen), type I IFN-related genes were up-regulated in only the IHNV DNA vaccinated group. The results presented here suggest that the IHNV DNA vaccine induces up-regulation of the type I IFN system across multiple tissues, which is the functional basis of early anti-viral immunity.

Dynamic regulation of IFN-gamma signaling in antigen-specific CD8+ T cells responding to infection

IFN-gamma plays a critical role in the CD8(+) T cell response to infection, but when and if this cytokine directly signals CD8(+) T cells during an immune response is unknown. We show that naive Ag-specific CD8(+) T cells receive IFN-gamma signals within 12 h after in vivo infection with Listeria monocytogenes and then become unresponsive to IFN-gamma throughout the ensuing Ag-driven expansion phase. Ag-specific CD8(+) T cells regain partial IFN-gamma responsiveness throughout the contraction phase, whereas the memory pool exhibits uniform, but reduced, responsiveness that is also modulated during the secondary response. The responsiveness of Ag-specific CD8(+) T cells to IFN-gamma correlated with modulation in the expression of IFN-gammaR2, but not with IFN-gammaR1 or suppressor of cytokine signaling-1. This dynamic regulation suggests that early IFN-gamma signals participate in regulation of the primary CD8(+) T cell response program, but that evading or minimizing IFN-gamma signals during expansion and the memory phase may contribute to appropriate regulation of the CD8(+) T cell response.