Background Women have an increased prevalence of severe asthma compared to men. IL-17A is associated with severe asthma and requires IL-23 receptor (IL-23R) signaling, which is negatively regulated by Let-7f miRNA. Objective Determine the mechanism by which 17β-estradiol (E2) and progesterone (P4) increase IL-17A production. Methods IL-17A production was determined by flow cytometry in Th17 cells from women (n=14) and men (n=15) with severe asthma. Cytokine levels were measured by ELISA and IL-23R and Let-7f expression by qPCR in Th17 differentiated cells from healthy women (n=13) and men (n=14). In sham-operated or ovariectomized female mice, 17β-E2, P4, 17β-E2+P4, or vehicle pellets were administered for 3 weeks prior to ex vivo Th17 cell differentiation. Airway neutrophil infiltration and KC expression was also determined in OVA-challenged WT female recipient mice with an adoptive transfer of OVA-specific Th17 cells from female and male mice. Results In severe asthma patients and healthy controls, IL-17A production was increased in Th17 cells from women compared to men. IL-23R expression was increased and Let-7f expression was decreased in Th17 differentiated cells from women compared to men. In ovariectomized mice, IL-17A and IL-23R expression was increased and Let-7f expression was decreased in the Th17 cells from mice administered 17β-E2+P4 compared to vehicle. Further, transfer of female OVA-specific Th17 cells increased acute neutrophil infiltration in the lungs of OVA-challenged recipient mice compared to transfer of male OVA-specific Th17 cells. Conclusions 17β-E2+P4 increased IL-17A production from Th17 cells, providing a potential mechanism for the increased prevalence of severe asthma in women compared to men.

Background IL-13 is a central mediator of airway responsiveness and mucus expression in allergic airway inflammation and IL-13 is currently a therapeutic target for asthma. However, little is known about how IL-13 regulates human CD4+ T cell lineages because the IL-13 receptor α1 (IL-13Rα1), a subunit of the IL-13 receptor, has not previously been reported to exist on human T cells. Objective To determine if human CD4+ Th17 cells express IL-13Rα1 and if IL-13 regulates Th17 cytokine production. Methods Naïve human CD4+ cells were isolated from whole blood, activated with anti-CD3 and anti-CD28, and polarized to Th1, Th2, Th17, or induced T regulatory cells in the presence of IL-13 (0–10ng/ml). Cell supernatants, total RNA, or total protein was examined four days after Th17 polarization. Results Th17 cells, but not Th0, Th1, Th2 or induced T regulatory cells, expressed IL-13Rα1. IL-13 attenuated IL-17A production as well as expression of RORC2, Runx1, and IRF-4 in Th17 polarized cells. IL-13 neither inhibited IFN-γ production from Th1 cells nor inhibited IL-4 production from Th2 cells. Furthermore, attenuation of IL-17A production only occurred when IL-13 was present within 24 hours of T cell activation or at the time of restimulation. Conclusions IL-13Rα1 is expressed on human CD4+ Th17 cells, and IL-13 attenuates IL-17A production at polarization and restimulation. While IL-13 is an attractive therapeutic target for decreasing symptoms associated with asthma, these results suggest that therapies inhibiting IL-13 production could have adverse side effects by increasing IL-17A production.

IL-13 is a central mediator of airway hyperreactivity and mucus expression, both hallmarks of asthma. IL-13 is found in the sputum of patients with asthma; therefore, IL-13 is an attractive drug target for treating asthma. We have previously shown that IL-13 inhibits Th17 cell production of IL-17A and IL-21 in vitro. Th17 cells are associated with autoimmune diseases, host immune responses, and severe asthma. In this study, we extend our in vitro findings and determine that IL-13 increases IL-10 production from Th17 polarized cells, and that IL-13-induced IL-10 production negatively regulates secretion of IL-17A and IL-21. To determine if IL-13 negatively regulates lung IL-17A expression via an IL-10 dependent mechanism in vivo, we used a model of respiratory syncytial virus (RSV) strain A2 infection in STAT1 KO mice which increases IL-17A and IL-13 lung expression, cytokines not produced during RSV infection in WT mice. To test the hypothesis that IL-13 negatively regulates lung IL-17A expression, we created STAT1/IL-13 double KO (DKO) mice. We found that RSV-infected STAT1/IL-13 DKO mice had significantly greater lung IL-17A expression compared to STAT1 KO mice, and increased IL-17A expression was abrogated by anti-IL-10 antibody treatment. RSV-infected STAT1/IL-13 DKO mice also had increased neutrophil infiltration RSV-infected STAT1 KO mice. Neutralizing IL-10 increased infiltration of inflammatory cells into the lungs of STAT1 KO mice but not STAT1/IL-13 DKO mice. These findings are vital to understanding potential side effects of therapeutics targeting IL-13. Inhibiting IL-13 may decrease IL-10 production and increase IL-17A production, thus potentiating IL-17A-associated diseases.

Background Viral infections are the most frequent cause of asthma exacerbations and are linked to increased airway reactivity (AR) and inflammation. Mice infected with respiratory syncytial virus (RSV) during ovalbumin (OVA)-induced allergic airway inflammation (OVA/RSV) had increased AR compared to OVA or RSV mice alone. Further, IL-17A was only increased in OVA/RSV mice. Objective To determine if IL-17A increases AR and inflammation in the OVA/RSV model. Methods Wild-type BALB/c and IL-17A KO mice underwent mock, RSV, OVA, or OVA/RSV protocols. Lungs, bronchoalveolar lavage (BAL) fluid, and/or mediastinal lymph nodes (MLNs) were harvested post infection. Cytokine expression was determined by flow cytometry and ELISA in the lungs or BAL fluid. MLNs were restimulated with either OVA (323–229) peptide or RSV M2 (127–135) peptide and IL-17A protein expression was analyzed. AR was determined by methacholine challenge. Results RSV increased IL-17A protein expression by OVA-specific T cells 6 days post infection. OVA/RSV mice had decreased IFN-α and IFN-β protein expression compared to RSV mice. OVA/RSV mice had increased IL-23 mRNA expression in lung homogenates compared to mock, OVA, or RSV mice. Unexpectedly, IL-17A KO OVA/RSV mice had increased AR compared to WT OVA/RSV mice. Further, IL-17A KO OVA/RSV mice had increased eosinophils, lymphocytes, and IL-13 protein expression in BAL fluid compared to WT OVA/RSV mice. Conclusions IL-17A negatively regulated AR and airway inflammation in OVA/RSV mice. This finding is important because IL-17A has been identified as a potential therapeutic target in asthma, and inhibiting IL-17A in the setting of virally induced asthma exacerbations may have adverse consequences.

BackgroundProstaglandin I2 (PGI2), a lipid mediator currently used in treatment of human disease, is a critical regulator of adaptive immune responses. Although PGI2 signaling suppressed Th1 and Th2 immune responses, the role of PGI2 in Th17 differentiation is not known.Methodology/Principal FindingsIn mouse CD4+CD62L+ naïve T cell culture, the PGI2 analogs iloprost and cicaprost increased IL-17A and IL-22 protein production and Th17 differentiation in vitro. This effect was augmented by IL-23 and was dependent on PGI2 receptor IP signaling. In mouse bone marrow-derived CD11c+ dendritic cells (BMDCs), PGI2 analogs increased the ratio of IL-23/IL-12, which is correlated with increased ability of BMDCs to stimulate naïve T cells for IL-17A production. Moreover, IP knockout mice had delayed onset of a Th17-associated neurological disease, experimental autoimmune encephalomyelitis (EAE), and reduced infiltration of IL-17A-expressing mononuclear cells in the spinal cords compared to wild type mice. These results suggest that PGI2 promotes in vivo Th17 responses.ConclusionThe preferential stimulation of Th17 differentiation by IP signaling may have important clinical implications as PGI2 and its analogs are commonly used to treat human pulmonary hypertension.

Mucous cell metaplasia is a hallmark of asthma, and may be mediated by signal transducers and activators of transcription (STAT)-6 signaling. IL-17A is increased in the bronchoalveolar lavage fluid of patients with severe asthma, and IL-17A also increases mucus production in airway epithelial cells. Asthma therapeutics are being developed that inhibit STAT6 signaling, but the role of IL-17A in inducing mucus production in the absence of STAT6 remains unknown. We hypothesized that IL-17A induces mucous cell metaplasia independent of STAT6, and we tested this hypothesis in two murine models in which increased IL-17A protein expression is evident. In the first model, ovalbumin (OVA)-specific D011.10 Th17 cells were adoptively transferred into wild-type (WT) or STAT6 knockout (KO) mice, and the mice were challenged with OVA or PBS. WT-OVA and STAT6 KO-OVA mice demonstrated increased airway IL-17A and IL-13 protein expression and mucous cell metaplasia, compared with WT-PBS or STAT6 KO-PBS mice. In the second model, WT, STAT1 KO, STAT1/STAT6 double KO (DKO), or STAT1/STAT6/IL-17 receptor A (RA) triple KO (TKO) mice were challenged with respiratory syncytial virus (RSV) or mock viral preparation, and the mucous cells were assessed. STAT1 KO-RSV mice demonstrated increased airway mucous cell metaplasia compared with WT-RSV mice. STAT1 KO-RSV and STAT1/STAT6 DKO-RSV mice also demonstrated increased mucous cell metaplasia, compared with STAT1/STAT6/IL17RA TKO-RSV mice. We also treated primary murine tracheal epithelial cells (mTECs) from WT and STAT6 KO mice. STAT6 KO mTECs showed increased periodic acid-Schiff staining with IL-17A but not with IL-13. Thus, asthma therapies targeting STAT6 may increase IL-17A protein expression, without preventing IL-17A-induced mucus production.Keywords: asthma; mucous cell metaplasia; IL-17A; STAT6; Airway mucus is a hallmark of asthma. Airway epithelial cell remodeling in asthma includes mucous cell metaplasia and mucus hypersecretion, which narrows the airway lumen and limits airflow (1). A major component of mucus consists of mucins, which are large glycoproteins that determine the viscoelasticity of mucus (2). Mucin genes are expressed in many tissues, but MUC5AC and MUC5B constitute the primary mucin genes expressed in the airway epithelial cells of the lung (3). Previous studies have shown that IL-13, a Th2 cytokine that is increased during allergic airway inflammation, is required for airway mucous cell metaplasia (4-7).IL-13 is abundant in the sputum of some patients with asthma (8). IL-13 binds to the IL-13 receptor (R), which is comprised of two subunits, IL-4Ra and IL-13Ra1. The binding of IL-13 to the IL-13R results in the phosphorylation and activation of the downstream transcription factor signal transducers and activators of transcription (STAT)-6 and the transcription of IL-13-mediated genes. STAT6 and IL-13 are required for maximal airway mucous cell metaplasia in murine models of allergic airway inflammation (4-6, 9). The airway instillation of recombinant IL-13 or t...

Prostaglandin (PG)I2 has important regulatory functions on the innate and adaptive immune systems. Recent experimental evidence reveals that PGI2 modulates the development and function of CD4+ T cells subsets, including Th1, Th2, and Th17 cell responses. In vitro and in vivo studies support that PGI2 generally has an inhibitory effect on Th1 and Th2 activation, differentiation, and cytokine production. In contrast, PGI2 seems to enhance Th17-favoring polarization conditions, resulting in Th17 cytokine production. Therefore, PGI2 may either promote or inhibit individual CD4+ cell subsets and impact adaptive immune responses.

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a multienzyme complex, is the major source for production of reactive oxygen species (ROS). ROS are increased in allergic diseases, such as asthma, but the role of ROS in disease pathogenesis remains uncertain. We hypothesized that mice unable to generate ROS via the NADPH oxidase pathway would have decreased allergic airway inflammation. To test this hypothesis, we studied gp91phox 2/2 mice in a model of allergic airway inflammation after sensitization and challenge with ovalbumin. Serum, bronchoalveolar lavage fluid, and lungs were then examined for evidence of allergic inflammation. We found that mice lacking a functional NADPH oxidase complex had significantly decreased ROS production and allergic airway inflammation, compared with wild-type (WT) control animals. To determine the mechanism by which allergic inflammation was inhibited by gp91phox deficiency, we cultured bone marrowderived dendritic cells from WT and gp91phox 2/2 mice and activated them with LPS. IL-12 expression was significantly increased in the gp91phox 2/2 bone marrow-derived dendritic cells, suggesting that the cytokine profile produced in the absence of gp91phox enhanced the conditions leading to T helper (Th) type 1 differentiation, while inhibiting Th2 polarization. Splenocytes from sensitized gp91phox 2/2 animals produced significantly less IL-13 in response to ovalbumin challenge in vitro compared with splenocytes from sensitized WT mice, suggesting that NADPH oxidase promotes allergic sensitization. In contrast, inflammatory cytokines produced by T cells cultured from WT and gp91phox 2/2 mice under Th0, Th1, Th2, and Th17 conditions were not significantly different. This study demonstrates the importance of NADPH oxidase activity and ROS production in a murine model of asthma.Keywords: asthma; allergic airway inflammation; gp91phox; reactive oxygen species; NADPH oxidase Asthma is a significant health problem, affecting up to 300 million children and adults around the world (1). In the United States alone, costs associated with asthma exceed $50 billion each year due to health care use and lost productivity (2). The prevalence of this disease is increasing, without clear etiology (3, 4). Chronic inflammation of the airways is a hallmark of the disease (5), and yet, despite widespread research, the mechanisms of persistent allergic airway inflammation are poorly understood.Reactive oxygen species (ROS) are increased in allergic diseases, such as asthma, and ROS production is associated with airway inflammation and airway hyperresponsiveness (6). Breath condensates from subjects with asthma have been shown to contain increased hydrogen peroxide, an ROS, and 8-isoprostane, an F 2 -isoprostane that is a marker of oxidative stress, compared to control subjects without asthma (7-9). In addition, increased levels of peroxidation products are present in the serum, urine, and lung tissue of patients with asthma compared with those without asthma (10-12). Mice with allergic lung inf...