Shi-Chuen Miaw

Cutting edge: IL-27 induces the transcription factor c-Maf, cytokine IL-21, and the costimulatory receptor ICOS that coordinately act together to promote differentiation of IL-10-producing Tr1 cells.

IL-27 has recently been identified as a differentiation factor for the generation of IL-10-producing regulatory type 1 (Tr1) T cells. However, how IL-27 induces the expansion of Tr1 cells has not been elucidated. In this study we demonstrate that IL-27 drives the expansion and differentiation of IL-10-producing murine Tr1 cells by inducing three key elements: the transcription factor c-Maf, the cytokine IL-21, and the costimulatory receptor ICOS. IL-27-driven c-Maf expression transactivates IL-21 production, which acts as an autocrine growth factor for the expansion and/or maintenance of IL-27-induced Tr1 cells. ICOS further promotes IL-27-driven Tr1 cells. Each of those elements is essential, because loss of c-Maf, IL-21-signaling, or ICOS decreases the frequency of IL-27-induced differentiation of IL-10-producing Tr1 cells.

The Cell Type-Specific Expression of the Murine IL-13 Gene Is Regulated by GATA-3

IL-13, a Th2 cell-specific cytokine, is a major effector molecule mediating several pathological features of allergic asthma. However, the transcriptional regulation of the IL-13 gene remains unclear. Here we demonstrate, by using intracellular cytokine staining, that IL-13 is not always coexpressed with other Th2 cytokines in normal Th cells on a single cell basis. In addition, we identified and cloned a minimal inducible and cell type-specific promoter of the murine IL-13 gene. The cell type specificity of the minimal IL-13 promoter is mediated by a functionally critical GATA-3 site that binds endogenous GATA-3 proteins, whereas the induction by PMA/ionomycin is mediated by distinct cis-acting elements. Furthermore, by expressing GATA-3 in wild-type and c-maf transgenic Th1 cells, we demonstrate that the expression of IL-13 is regulated by a mechanism distinct from that regulating the expression of IL-4, and that the expression of Th1 and Th2 cytokine genes does not have to be mutually exclusive in effector Th cells.

ROG, Repressor of GATA, Regulates the Expression of Cytokine Genes

GATA-3 is a T cell-specific transcription factor and is essential for the development of the T cell lineage. Recently, it was shown that the expression of GATA-3 is further induced in CD4+ helper T cells upon differentiation into type 2 but not type 1 effector cells. Here, we report the molecular cloning of a GATA-3 interacting protein, repressor of GATA (ROG). ROG is a lymphoid-specific gene and is rapidly induced in Th cells upon stimulation with anti-CD3. In in vitro assays, ROG represses the GATA-3-induced transactivation. Furthermore, overexpression of ROG in Th clones inhibits the production of Th cytokines. Taken together, our results suggest that ROG might play a critical role in regulating the differentiation and activation of Th cells.

Concurrent exposure to a dectin-1 agonist suppresses the Th2 response to epicutaneously introduced antigen in mice.

BackgroundEpicutaneous sensitization with protein allergen that induces predominant Th2 responses is an important sensitization route in atopic dermatitis. Fungal components have been shown to modulate Th cell differentiation. However, the effects of fungal components on epicutaneous sensitization are unclear.ResultsIn this study, we showed that co-administration of curdlan, a dectin-1 agonist, during epicutaneous ovalbumin sensitization of BALB/c mice decreased the IL-5 and IL-13 levels in supernatants of lymph node cell ovalbumin reactivation cultures. Mechanistically, curdlan co-administration decreased IL-4 and IL-1β expressions in draining lymph nodes. Curdlan co-administration also lower the migration of langerin+ CD103- epidermal Langerhans cells into draining lymph nodes at 96 hours post-sensitization which might be attributed to decreased expressions of IL-18 and IL-1β in patched skin. Moreover, adoptive transfer of CFSE-labeled transgenic CD4 T cells confirmed that curdlan co-administration decreased the proliferation and IL-4-production of ovalbumin -specific T cells primed by epidermal Langerhans cells.ConclusionsThese results indicated that concurrent exposure to a dectin-1 agonist suppresses the epicutaneously induced Th2 response by modulating the cytokine expression profiles in draining LNs and the migration of epidermal Langerhans cells. These results highlight the effects of fungal components on epicutaneous allergen sensitization in atopic diseases.

Galectin-3 Negatively Regulates Dendritic Cell Production of IL-23/IL-17–Axis Cytokines in Infection by Histoplasma capsulatum

Galectin-3 (gal3) is known for its immunoregulatory functions in infectious, autoimmune, and inflammatory diseases. However, little is known about its regulatory role in the hosts IL-17A response to infection. Using a mouse model of histoplasmosis in which both Th1 and Th17 responses contribute to fungal clearance, we investigated how gal3 regulates IL-17A responses. Our study showed that Histoplasma infection induced gal3−/− dendritic cells to produce significantly higher levels of IL-23, TGF-β1, and IL-1β than did gal3+/+ cells. Infected by the same inoculum of Histoplasma, gal3−/− mice had lower fungal burden and produced higher levels of IL-23/IL-17–axis cytokines and lower levels of IL-12 and IFN-γ. Additionally, there was an increase in Th17 cells and a reduction in Th1 cells in infected gal3−/− mice. In vitro Th1/Th17-skewing experiments excluded the intrinsic effect of gal3 on Th cell differentiation. Although neutrophils from both gal3+/+ and gal3−/− mice produced IL-17A upon IL-23 stimulation, their contribution to IL-17A production was greater in gal3−/− mice than in gal3+/+ mice. Compared with gal3+/+ dendritic cells, adoptive transfer of gal3−/− dendritic cells resulted in production of significantly higher levels of IL-17–axis cytokines and reduced fungal burden. It appears that reduced fungal burden and preferential IL-17A response in gal3−/− mice by both Th17 cells and neutrophils were the result of preferential production of IL-23/IL-17–axis cytokines by dendritic cells. Our study showed that gal3 negatively regulates IL-17A responses through inhibition of IL-23/IL-17–axis cytokine production by dendritic cells.

PTPN22 Modulates Macrophage Polarization and Susceptibility to Dextran Sulfate Sodium–Induced Colitis

PTPN22, a protein tyrosine phosphatase expressed mainly in hematopoietic cells, has been linked to many autoimmune diseases. A C-to-T single nucleotide polymorphism (SNP) at position 1858 of human PTPN22 cDNA decreases the risk of Crohn’s disease. However, the function of PTPN22 and the mechanism by which this SNP reduces the risk of Crohn’s disease are poorly understood. We find that PTPN22 is expressed in macrophages. It suppresses M1 macrophage polarization and reciprocally promotes the expression of M2-associated genes. PTPN22-deficient mice develop severe colitis induced by dextran sulfate sodium, and their intestinal macrophages express higher levels of M1 genes but lower levels of M2-associated genes. Furthermore, the protective T allele of the C1858T SNP is associated with attenuated expression of inflammatory cytokines and a higher level of PTPN22 in human M1 macrophages. This T allele–associated aberrant expression of PTPN22 is partly attributed to an autoinhibition mechanism, in which PTPN22 suppresses its own expression in M1 but not M2 macrophages. Our data not only demonstrate a critical role of PTPN22 in regulating macrophage polarization but also provide a molecular explanation for the protective effect of the C1858T SNP in Crohn’s disease.

ROG Negatively Regulates T-Cell Activation but Is Dispensable for Th-Cell Differentiation

ABSTRACT ROG, a transcriptional repressor, is a direct target gene of NF-AT and a putative negative regulator of T-cell activation. In addition, overexpression of ROG suppresses the activity of GATA-3, implying a role of ROG in the differentiation and function of Th cells. Despite these observations, the function of ROG has yet to be confirmed by loss-of-function approaches. Here we report that ROG-deficient T cells are hypersensitive to anti-CD3 stimulation and produce more interleukin-2 (IL-2) due to enhanced NF-κB activity. ROG-deficient dendritic cells also produce more IL-12p40, another NF-κB target gene. However, ROG-deficient Th cells are capable of differentiating into Th1 and Th2 cells, and ROG-deficient mice have no defect in mounting appropriate Th immune responses in vivo. Thus, ROG is dispensable for the differentiation and function of Th cells but serves as a mediator of NF-AT-initiated suppression of NF-κB. Its mechanism of action and its expression pattern are distinct from those of other transcription factors negatively regulating the activation of T cells.

Different Modulation of Ptpn22 in Effector and Regulatory T Cells Leads to Attenuation of Autoimmune Diabetes in Transgenic Nonobese Diabetic Mice

Ptpn22 encodes PEST domain–enriched tyrosine phosphatase (Pep), which negatively regulates TCR proximal signaling and is strongly associated with a variety of autoimmune diseases in humans. The net effect of Pep on the balance of immunity and tolerance is uncertain because of the simultaneous inhibition of TCR-mediated signaling of effector and regulatory T cells (Tregs). In this study, we generated transgenic NOD mice that overexpressed Pep in T cells. The transgenic mice had a significantly lower incidence of spontaneous autoimmune diabetes, which was accompanied by fewer IFN-γ–producing T cells, and an increased ratio of CD4+Foxp3+ Tregs to CD4+IFN-γ+ or to CD8+IFN-γ+ T cells, respectively, in pancreatic islets. Transgenic T cells showed markedly decreased TCR-mediated effector cell responses such as proliferation and Th1 differentiation. By contrast, the inhibitory effect of transgenic Pep on TCR signaling did not affect the differentiation of Tregs or their suppressive activity. Adoptive transfer experiments showed that transgenic splenocytes exhibited attenuated diabetogenic ability. To examine further the pathogenic features of transgenic T cells, we generated Ptpn22/BDC2.5 doubly transgenic mice and found reduced proliferation and Th1 differentiation in CD4+ T lymphocytes with additional Pep in pancreatic lymph nodes but not in inguinal lymph nodes of NOD/SCID recipients. This finding indicates that transgenic Pep attenuates T cell functions in an islet Ag–driven manner. Taken together, our results demonstrate that Pep overexpression in T cells attenuates autoimmune diabetes in NOD mice by preferentially modulating TCR signaling–mediated functions in diabetogenic T cells but not in Tregs.

Galectin-3 Modulates Th17 Responses by Regulating Dendritic Cell Cytokines

Galectin-3 is a β-galactoside-binding animal lectin with diverse functions, including regulation of T helper (Th) 1 and Th2 responses. Current data indicate that galectin-3 expressed in dendritic cells (DCs) may be contributory. Th17 cells have emerged as critical inducers of tissue inflammation in autoimmune disease and important mediators of host defense against fungal pathogens, although little is known about galectin-3 involvement in Th17 development. We investigated the role of galectin-3 in the induction of Th17 immunity in galectin-3-deficient (gal3(-/-)) and gal3(+/+) mouse bone marrow-derived DCs. We demonstrate that intracellular galectin-3 negatively regulates Th17 polarization in response to the dectin-1 agonist curdlan (a β-glucan present on the cell wall of fungal species) and lipopolysaccharide, agents that prime DCs for Th17 differentiation. On activation of dectin-1, gal3(-/-) DCs secreted higher levels of the Th17-axis cytokine IL-23 compared with gal3(+/+) DCs and contained higher levels of activated c-Rel, an NF-κB subunit that promotes IL-23 expression. Levels of active Raf-1, a kinase that participates in downstream inhibition of c-Rel binding to the IL23A promoter, were impaired in gal3(-/-) DCs. Modulation of Th17 by galectin-3 in DCs also occurred in vivo because adoptive transfer of gal3(-/-) DCs exposed to Candida albicans conferred higher Th17 responses and protection against fungal infection. We conclude that galectin-3 suppresses Th17 responses by regulating DC cytokine production.

PTPN22.6, a Dominant Negative Isoform of PTPN22 and Potential Biomarker of Rheumatoid Arthritis

PTPN22 is a tyrosine phosphatase and functions as a damper of TCR signals. A C-to-T single nucleotide polymorphism (SNP) located at position 1858 of human PTPN22 cDNA and converting an arginine (R620) to tryptophan (W620) confers the highest risk of rheumatoid arthritis among non-HLA genetic variations that are known to be associated with this disease. The effect of the R-to-W conversion on the phosphatase activity of PTPN22 protein and the impact of the minor T allele of the C1858T SNP on the activation of T cells has remained controversial. In addition, how the overall activity of PTPN22 is regulated and how the R-to-W conversion contributes to rheumatoid arthritis is still poorly understood. Here we report the identification of an alternative splice form of human PTPN22, namely PTPN22.6. It lacks the nearly entire phosphatase domain and can function as a dominant negative isoform of the full length PTPN22. Although conversion of R620 to W620 in the context of PTPN22.1 attenuated T cell activation, expression of the tryptophan variant of PTPN22.6 reciprocally led to hyperactivation of human T cells. More importantly, the level of PTPN22.6 in peripheral blood correlates with disease activity of rheumatoid arthritis. Our data depict a model that can reconcile the conflicting observations on the functional impact of the C1858T SNP and also suggest that PTPN22.6 is a novel biomarker of rheumatoid arthritis.