An altered balance between Th1 and Th2 cytokines is responsible for a variety of immuno-inflammatory disorders such as asthma, yet the role of post-transcriptional mechanisms, such as those mediated by microRNAs, in adjusting the relative magnitude and balance of Th cytokine expression have been largely unexplored. Here we show that miR-21 has a central role in setting a balance between Th1 and Th2 responses to antigens. Targeted ablation of miR-21 in mice led to reduced lung eosinophilia after allergen challenge, with a broadly reprogrammed immunoactivation transcriptome, and significantly increased levels of the Th1 cytokine IFNγ. Biological network-based transcriptome analysis of OVA-challenged miR-21-/-mice identified an unexpected prominent dysregulation of IL-12/IFNγ pathways as the most significantly affected in the lungs with a key role for miR-21 in IFNγ signaling and T-cell polarization, consistent with a functional miR-21 binding site in IL-12p35. In support of these hypotheses, miR-21 deficiency led dendritic cells to produce more IL-12 after LPS stimulation, and OVA-challenged CD4+ T lymphocytes to produce increased IFNγ and decreased IL-4. Further, loss of miR-21 significantly enhanced the Th1-associated delayed-type hypersensitivity cutaneous responses. Thus, our results define miR-21 as a major regulator of Th1 vs. Th2 responses, defining a new mechanism for regulating polarized immuno-inflammatory responses.

Background: Resistin-like molecule (Relm) α is a secreted protein and a hallmark signature gene for alternatively activated macrophages. Relm-α is highly induced by allergic inflammatory triggers and perceived to promote tissue repair. Yet the function of Relm-α remains unknown. Objective: We sough to determine the role of Relm-α in dextran sodium sulfate (DSS)–induced colonic injury. Methods: The cellular source of Relm-α was determined after oral DSS-induced colitis. Retnla−/− mice were generated, subjected to DSS treatment, and monitored for disease progression (clinical and histopathologic features). Cytokine production in the supernatants of ex vivo colon cultures, and of LPS-stimulated macrophages incubated with Relm-α was assessed. Relm-α was administered intraperitoneally, and the cellular recruitment to the peritoneum was assessed. Results: After innate intestinal stimulation with DSS, Relm-α was highly expressed by eosinophils and epithelial cells. Retnla gene–targeted mice were protected from DSS-induced colitis (eg, decreased diarrhea, rectal bleeding, colon shortening, disease score, and histopathologic changes). Relm-α coactivated IL-6 and TNF-α release and inhibited IL-10 release from LPS-activated bone marrow–derived macrophages. Consistent with these finding, colon cultures of DSS-treated Retnla−/− mice produced decreased IL-6 and increased IL-10 ex vivo. Furthermore, Retnla−/− mice had substantially decreased c-Jun N-terminal kinase phosphorylation in vivo. In vivo administration of Relm-α initiated cellular recruitment to the peritoneum, and Relm-α was able to induce eosinophil chemotaxis in vitro. Conclusions: These findings demonstrate a central proinflammatory role for Relm-α in colonic innate immune responses, identifying a novel pathway for regulation of macrophage activation.

Resistin-like molecule α (Relm-α) is a secreted cysteine-rich protein belonging to a newly defined family of proteins, including resistin, Relm-β, and Relm-γ. Resistin was initially defined based on its insulin resistance activity, but the family members are highly up-regulated in various inflammatory states, especially those involving intestinal inflammation. In this study, we report the role of Relm-α at baseline and following an experimental model of colitis. Relm-α was readily detected in the serum at baseline (4–5 ng/ml), and its level was regulated by energy uptake. Retnla−/− mice had decreased baseline circulating leptin levels, but displayed normal glucose, glucose clearance, and insulin levels. Following exposure to the oral innate trigger dextran sodium sulfate (DSS), a nonredundant proinflammatory role for Relm-α was uncovered as Retnla−/− mice were markedly protected from DSS-induced disease activity and histopathological features. Relm-α regulated eosinophil-directed cytokines (e.g., IL-5, CCL11/eotaxin-1, and CCL5/RANTES) and IL-17 ex vivo. Consistently, DSS-treated Retnla−/− mice displayed substantially decreased eosinophil accumulation and decreased phosphorylation of NF-κB, ERK1/2, and p38 in macrophages and eosinophils. Following DSS exposure, serum level of Relm-α was up-regulated, and DSS-treated Retnla−/− mice were markedly protected from hyperglycemia induced by glucose injection independent of changes in insulin levels. Retnla−/− mice were protected from increases in gut hormone serum levels of gastric inhibitory polypeptide and peptide YY that were induced following DSS treatment. These findings demonstrate a central proinflammatory role for Relm-α in the regulation of colonic inflammation and a novel link between colonic injury, glucose tolerance, and energy intake.

Interleukin (IL)-13 and IL-4 are hallmark cytokines of Th2-associated diseases including asthma. Recent studies revealed that IL-13Rα1 regulates asthma pathogenesis by mediating both IL-4 and IL-13-mediated responses. Nonetheless, the relative contribution of each cytokine in response to aeroallergen challenge and the degree of functional dichotomy between IL-4 and IL-13 in asthma remains unclear. Consistent with prior publications, we demonstrate that IL-13Rα1 regulates aeroallergen-induced airway resistance and mucus production but not IgE and Th2 cytokine production. We demonstrate that aeroallergen-induced eosinophil recruitment and chemokine production were largely dependent of IL-13Rα1 following Aspergillus (Asp) but not house dust mite (HDM) challenges. Notably, Asp-challenged mice displayed increased IL-13Rα1-dependent accumulation of dendritic cell subsets into lung draining lymph nodes in comparison with HDM. Comparison of IL-4 and IL-13 levels in the different experimental models revealed increased IL-4:IL-13 ratios following HDM challenge, likely explaining the IL-13Rα1-independent eosinophilia and chemokine production. Consistently, eosinophil adoptive-transfer experiments revealed near ablation of lung eosinophilia in response to Asp in Il13ra1−/− mice, suggesting that Asp-induced lung eosinophil recruitment is regulated by IL-13-induced chemokine production, rather than altered IL-13 signaling in eosinophils. Furthermore, the near complete protection observed in Il13ra1−/− mice in response to Asp-challenge was dependent on mucosal sensitization since Alum/Asp-sensitized mice that were re-challenged with Asp developed IL-13Rα1-independent eosinophilia although other asthma parameters remained IL-13Rα1-dependent. These results establish that IL-13Rα1 is required for aeroallergen-induced airway resistance and that allergen-induced chemokine production and consequent eosinophilia is dictated by the balance between IL-4 and IL-13 production in situ.

Background & Aims Innate and adaptive immune responses are regulated by crosstalk between activation and inhibitory signals. Dysregulation of the inhibitory signal can lead to aberrant chronic inflammatory diseases such as the inflammatory bowel diseases (IBD). Little is known about negative regulation of innate intestinal immune activation. We examined the role of the inhibitory receptor paired immunoglobulin-like receptor B (PIR-B) in the regulation of macrophage function in innate intestinal immunity. Methods We examined the susceptibility of Pirb-/- and wild-type (WT) mice to dextran sodium sulfate (DSS)-induced colitis. We assessed proinflammatory cytokine release and MAPK and NFκB activation in Pirb-/- and WT macrophages following E. coli stimulation. Macrophage transfer experiments were performed to define the role of PIR-B in the negative regulation of macrophage function in DSS-induced colitis. We also assessed expression of PIR-B human homologs (ILT-2 and ILT-3) in colon biopsy samples from healthy individuals (controls) and patients with IBD. Results Pirb-/- mice had increased susceptibility to DSS-induced colitis. In vitro analysis demonstrated increased production of proinflammatory cytokines (IL-6, IL-1β and TNF-α) and activation of MAPK and NFκB in Pirb-/- macrophages following bacterial activation. Adoptive transfer of bone marrow-derived Pirb-/- macrophages into WT mice was sufficient to increase disease susceptibility. ILT-2 and ILT-3 were expressed on CD68+ and CD68- mononuclear cells and intestinal epithelium in colon biopsy samples from patients and controls. Conclusions PIR-B negatively regulates macrophage functions in response to pathogenic bacteria and chronic intestinal inflammatory responses. Inhibitory receptors such as PIR-B might be used as therapeutic targets for treatment of patients with IBD.

Resistin-like molecule a (Relm-a) is one of the most up-regulated gene products in allergen-and parasite-associated Th2 responses. Localized to alternatively activated macrophages, Relm-a was shown to exert an anti-inflammatory effect in parasite-induced Th2 responses, but its role in experimental asthma remains unexplored. Here, we analyzed the cellular source, the IL-4 receptors required to stimulate Relm-a production, and the role of Relm-a after experimental asthma induction by IL-4, IL-13, or multiple experimental regimes, including ovalbumin and Aspergillus fumigatus immunization. We demonstrate that Relm-a was secreted into the airway lumen, dependent on both the IL-13 receptora1 chain and likely the Type I IL-4 receptor, and differentially localized to epithelial cells and myeloid cells, depending on the specific cytokine or aeroallergen trigger. Studies performed with Retnla gene-targeted mice demonstrate that Relm-a was largely redundant in terms of inducing the infiltration of Th2 cytokines, mucus, and inflammatory cells into the lung. These results mirror the dispensable role that other alternatively activated macrophage products (such as arginase 1) have in allergen-induced experimental asthma and contrast with their role in the setting of parasitic infections. Taken together, our findings demonstrate the distinct utilization of IL-4/IL-13 receptors for the induction of Relm-a in the lungs. The differential regulation of Relm-a expression is likely determined by the relative expression levels of IL-4, IL-13, and their corresponding receptors, which are differentially expressed by divergent cells (i.e., epithelial cells and macrophages.) Finally, we identify a largely redundant functional role for Relm-a in acute experimental models of allergen-associated Th2 immune responses.Keywords: resistin-like molecule-a; asthma; IL-4; Asthma is a chronic and complex inflammatory disease of the airways characterized by airflow obstruction, mucus production, airway hyperresponsiveness (AHR), and airway inflammation. It is the most common chronic illness of childhood, affecting up to 20% of children and 7% of adults in Western countries, with a combined prevalence of approximately 300 million people worldwide (1).Asthmatic responses are associated with increased numbers of pulmonary inflammatory cells, including activated T-lymphocytes and eosinophils, which correlate with disease severity (2, 3). T-lymphocytes of the Th2 phenotype are thought to induce asthma through the secretion of an array of cytokines, and in particular, IL-4 and IL-13 (4, 5). These cytokines are produced at elevated concentrations in allergic tissue, and are central regulators of many hallmark features of the disease, such as the production of IgE, Th2 differentiation, eosinophilia, mucus hypersecretion, chemokine induction, and airway hyperresponsiveness (AHR) (6). Notably, IL-13 is considered more of an effector cytokine in the pathogenesis of allergic airway disease compared with IL-4 because AHR and mucus production are predominantly I...

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Mixed Lineage Kinase 3 (MLK3) is a mitogen activated protein kinase kinase kinase (MAP3K) that activates multiple MAPK signaling pathways. Nuclear factor kappa B (NF-κB) is a transcription factor that has important functions in inflammation, immunity and cell survival. We found that silencing mlk3 expression with RNA interference (RNAi) in SKOV3 human ovarian cancer epithelial cells and NIH-3T3 murine fibroblasts led to a reduction in the level of the inhibitor of kappa B alpha (IκBα) protein. In addition, we observed enhanced basal IκB kinase (IKK) activity in HEK-293 cells transiently transfected with MLK3 siRNA and in NIH3T3 cells stably expressing MLK3 shRNA (shMLK3). Furthermore, the basal level of NF-κB-dependent gene transcription was elevated in shMLK3 cells. Silencing mlk3 expression conferred resistance of cells to etoposide-induced apoptotic cell death and overexpression of wild type MLK3 (MLK3-WT) or kinase-dead MLK3 (MLK3-KD) promoted apoptotic cell death and cleavage of poly (ADP-ribose) polymerase (PARP). Overexpression of MLK3-WT or MLK3-KD enhanced etoposide-induced apoptotic cell death and cleavage of PARP. These data suggest that MLK3 functions to limit IKK activity, and depleting MLK3 helps protect cells from etoposide-induced cell death through activation of IKK-dependent signaling.