Published On: Tue, Jan 15th, 2019

IL-31 plays dual roles in lung inflammation in an OVA-induced murine asthma model [RESEARCH ARTICLE]

DISCUSSION

In this study, we first investigated IL-31 levels in peripheral blood and expression of IL-31RA in the lungs of mice undergoing allergic airway inflammation following 8 consecutive weeks of intranasal challenge with OVA. The results demonstrated that higher levels of IL-31 in peripheral blood and elevated IL-31 mRNA in lungs persistently existed during 2 months of airway inflammation, although with a slight decrease at later time-points as compared with those at day 28, indicating that IL-31 modulated the development of airway inflammation in asthma. It has been reported that an increase in IL-31 levels was detected in patients with allergic rhinitis and IL-31 induced production of IL-4, IL-5 and IL-13 in PBMC and nasal epithelial cells from patients with allergic rhinitis (Stott et al., 2013). Serum IL-31 levels were significantly elevated in patients with asthma and correlated positively with Th2 type cytokines IL-5 and IL-13, asthma severity or total serum IgE (Lai et al., 2016). Previous studies demonstrated that IL-31 induced the production of inflammatory cytokines and chemokines in human primary keratinocytes, monocytes/macrophages and bronchial epithelial cells, which was enhanced by IL-4 and IL-13 (Ip et al., 2007; Kasraie et al., 2011; Kasraie et al., 2010). These data suggest that IL-31 may positively regulate the inflammation of Th2 type diseases via induction of chemokines, which recruit infiltrates in local tissue.

We also found that IL-31RA mRNA was elevated in lungs throughout 8 consecutive weeks of allergic airway inflammation following OVA challenge as compared with PBS control, indicating consecutive elevated IL-31R signaling in lungs. It has been reported that IL-31 induced expression of chemokines contributing to airway inflammation and tissue damage in human bronchial epithelial BEAS-2B cells (Ip et al., 2007). To determine whether IL-31 stimulates the production of inflammatory cytokines and chemokines in lung epithelial cells, type II alveolar epithelial cells isolated from mice were stimulated with recombinant mouse IL-31 and RNA was extracted for analysis of cytokines and chemokines by gene array chip. An increase in expression of 19 gene was found in IL-31-treated cells, some of which are related to the migration of eosinophils, T cells and monocytes/macrophages, including CCL5, CCL6, CCL11, CCL16, CCL22, CCL28 and CX3CL1 (Isgro et al., 2013; Rose et al., 2010; Matsukura et al., 2010; Viney et al., 2014; Ooi et al., 2012). Consistent with this, we also found that chemokine receptors mRNA, such as CCR1, CCR3, CCR5, CXCR1, CXCR2 and CXCR6, were increased in alveolar epithelial cells after IL-31 stimulation. In addition, the migration of macrophages and T cells was increased by supernatants of alveolar cells stimulated with IL-31 in a time-dependent manner. These data demonstrated that IL-31 promoted lung inflammation in allergic asthma via induction of chemokines in alveolar epithelial cells. However, anti-IL-31 antibodies did not neutralize the production of Th2 type cytokines either in vitro or in vivo mouse models of allergic asthma (Bilsborough et al., 2010). One explanation is that IL-31 is one of these Th2-type cytokines that induce inflammation-related cytokines, such as IL-4, IL-5 and IL-13, which form the complex network of cytokines that governs the development allergic asthma and so that role of IL-31 may be covered by other stronger cytokines.

IL-31RA expression has been detected on a wide range of cell types including macrophages, mast cells, T cells, and epithelial cells (Dillon et al., 2004; Diveu et al., 2004; Dreuw et al., 2004; Yamaoka et al., 2009) and IL-31 is produced by activated CD4+ T cells, eosinophils, macrophages and dendritic cells (Dillon et al., 2004; Kunsleben et al., 2015; Cornelissen et al., 2011). Loss of IL-31R signaling in IL-31RA KO mice resulted in exacerbated inflammation, increased IgE levels and IL-4-positive infiltrates, and more IL-4 and IL-13 secreted by draining lymph nodes cells after OVA sensitization and challenge, indicating an enhanced Th2 response in antigen-challenged IL-31RA KO mice. This is consistent with the findings that parasites induced exacerbated Th2 type inflammation in lung and intestines of mice deficient in IL-31RA, and CD4+ T cells from IL-31RA KO mice exhibited enhanced proliferation (Perrigoue et al., 2007; Perrigoue et al., 2009). However, Bilsborough et al. (Bilsborough et al., 2010) reported that IL-31 receptor KO mice exhibited elevated responsiveness to oncostatin M. They also found that IL-31RA KO mice had significantly increased percentages of neutrophil and lymphocyte populations before OVA stimulation, compared with WT mice. In contrast, in our study, no increase in infiltrates was detected in BALF collected from naïve mice deficient in IL-31RA. However, we did observe enhanced proliferation of CD4+ T cells in IL-31RA KO mice, whereas no difference in the activation of CD4+ T cells was found between WT and IL-31RA KO mice. Th2 and recently reported Th17 subsets have been implicated in the regulation of many immune responses linked to lung inflammation in patients with asthma (Zhou et al., 2017). To address the question of whether IL-31 influences the differentiation of Th2 and Th17, naïve CD4+ T cells were stimulated with anti-CD3/anti-CD28 under neutral or Th1-, Th2-, Th17- polarizing condition. No difference in the expression of cytokines IFN-γ, IL-4, IL-17 and transcription factors T-bet, GATA-3, ROR-γt in CD4+ T cells was observed between naïve WT and IL-31RA KO mice after stimulation of CD4+ T cells with anti-CD3/anti-CD28 under neutral or Th1-, Th2-, Th17- polarizing conditions. These data demonstrate that IL-31-IL-31R interaction negatively regulates lung inflammation in asthma through induction of proliferation of CD4+ T cell and production of Th2 effector cytokines, not promotion of CD4+ T cell subset differentiation.

Most cytokines have the ability to mediate pleiotropic effects, depending on the cytokine milieu and tissues in which their receptors are expressed (Hunter and Kastelein, 2012; Fontes et al., 2015; Tamasauskiene and Sitkauskiene, 2017; Fisher et al., 2014). It has become clear that many IL-6 family cytokines suppress inflammatory responses, although many that signal through gp130 have critical proinflammatory effects (Chen et al., 2017; Pyle et al., 2017; Su et al., 2016). IL-27 can promote Th1 responses via augmenting proliferation and secretion of IFN-γ by naïve CD4+ T cells (Yoshimoto et al., 2007; Pflanz et al., 2002; Chen et al., 2000). However, IL-27ra−/− mice infected with Toxoplasma gondii generated an IFN-γ response to limit parasite replication, and subsequently developed lethal CD4+ T cell mediated inflammation (Artis et al., 2004a; Artis et al., 2004b; Batten et al., 2006; Miyazaki et al., 2005; Stumhofer et al., 2006). IL-31RA is a novel member of the gp130-subfamily, sharing the conserved structural motifs of type I cytokine receptor and mediates IL-31 signaling when coupled with OSMR (Dillon et al., 2004; Diveu et al., 2004). IL-31 binding with the IL-31RA/OSMRB complex activates the JAK/STAT signaling pathway, which involves STAT1, STAT3 and STAT5 phosphorylation (Dambacher et al., 2007; Kasraie et al., 2013). STAT3 activation by IL-31 induces the expression of SOCS3, which inhibits further IL-31 signaling in a negative feedback loop, through inhibition of JAK activity (Maier et al., 2015). As a novel member of IL-6 family, IL-31 may have dual roles due to the complex of its heterodimer receptor and cytokine milieu, acting as an early proinflammatory regulator and subsequent negative feedback pathway for suppressing the magnitude of type 2 inflammation.

In summary, we first demonstrated that IL-31 promoted lung inflammation in allergic asthma mice via inducing production of chemokines in alveolar epithelial cells to recruit cell infiltrates. Our results from an asthma model using IL-31RA KO mice showed that IL-31R signaling negatively regulates inflammation through suppressing the proliferation of CD4+ T cells, which led to the decreased production of Th2-type cytokines. These data indicated that IL-31 may play dual roles, first an early proinflammation Th2 response followed by a later negative feedback response, associated with allergic asthma. Although our study demonstrated that IL-31-IL-31R interaction does not influence the differentiation of Th1, Th2 and Th17, the role of IL-31 in suppression or induction of Treg responses remains to be examined. Moreover, while much of the early work has attempted to identify the function of IL-31 in isolation, it is likely that the effects of IL-31R signaling are regulated by other pro- and anti-inflammatory cytokines.

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