IL-33 and IgE stimulate mast cell production of IL-2 and regulatory T cell expansion in allergic dermatitis

BACKGROUND

We have previously shown that mast cells (MCs) suppress chronic allergic dermatitis in mice. The underlying mechanism involves MC-derived IL-2, which supports regulatory T cell (Treg) response at the site of inflammation. However, it is not clear what are the factors that drive MCs to produce IL-2.

OBJECTIVE

To understand the mechanisms that lead to IL-2 production from MCs in chronic allergic dermatitis.

METHODS

Isolated murine bone marrow-derived MCs (BMMCs) were incubated with various stimulators, and IL-2 production was assessed by RT-PCR and ELISA. The response of signalling pathways was evaluated by MAPK inhibitors and Western blot analysis. The effect of MC-IL-2 on Tregs was studied by incubation of splenic T cells with conditioned media obtained from activated BMMCs. Dermatitis was elicited by repeated exposures of mouse ears to oxazolone. MCs in mouse and human skin samples were evaluated by immunostaining.

RESULTS

BMMCs released IL-2 in response to IL-33, and IL-2 production was further enhanced by concomitant FcεRI activation. The effect of IL-33 was mediated by activation of the MAPK family members. IL-2 in conditioned media from IL-33 and IgE-stimulated BMMCs led to considerable expansion of Tregs in vitro. IL-33 levels were elevated in oxazolone-challenged ears along with increased numbers of IL-2-expressing MCs. Human skin with chronic inflammation also contained IL-2-expressing MCs that colocalized with IL-33 staining in the dermis.

CONCLUSIONS

IL-33, in collaboration with IgE, is critical for MC-IL-2 production in allergic skin disease, thus leading to Treg stimulation and suppression of allergic dermatitis.

A key requirement for CD300f in innate immune responses of eosinophils in colitis

Eosinophils are traditionally studied in the context of type 2 immune responses. However, recent studies highlight key innate immune functions for eosinophils especially in colonic inflammation. Surprisingly, molecular pathways regulating innate immune activities of eosinophil are largely unknown. We have recently shown that the CD300f is highly expressed by colonic eosinophils. Nonetheless, the role of CD300f in governing innate immune eosinophil activities is ill-defined. RNA sequencing of 162 pediatric Crohn's disease patients revealed upregulation of multiple Cd300 family members, which correlated with the presence of severe ulcerations and inflammation. Increased expression of CD300 family receptors was also observed in active ulcerative colitis (UC) and in mice following induction of experimental colitis. Specifically, the expression of CD300f was dynamically regulated in monocytes and eosinophils. Dextran sodium sulfate (DSS)-treated Cd300f^-/- mice exhibit attenuated disease activity and histopathology in comparison with DSS-treated wild type (WT). Decreased disease activity in Cd300f^-/- mice was accompanied with reduced inflammatory cell infiltration and nearly abolished production of pro-inflammatory cytokines. Monocyte depletion and chimeric bone marrow transfer experiments revealed a cell-specific requirement for CD300f in innate immune activation of eosinophils. Collectively, we uncover a new pathway regulating innate immune activities of eosinophils, a finding with significant implications in eosinophil-associated gastrointestinal diseases.

A protective role for IL-13 receptor α 1 in bleomycin-induced pulmonary injury and repair

Molecular mechanisms that regulate lung repair vs. progressive scarring in pulmonary fibrosis remain elusive. Interleukin (IL)-4 and IL-13 are pro-fibrotic cytokines that share common receptor chains including IL-13 receptor (R) α1 and are key pharmacological targets in fibrotic diseases. However, the roles of IL-13Rα1 in mediating lung injury/repair are unclear. We report dysregulated levels of IL-13 receptors in the lungs of bleomycin-treated mice and to some extent in idiopathic pulmonary fibrosis patients. Transcriptional profiling demonstrated an epithelial cell-associated gene signature that was homeostatically dependent on IL-13Rα1 expression. IL-13Rα1 regulated a striking array of genes in the lung following bleomycin administration and Il13ra1 deficiency resulted in exacerbated bleomycin-induced disease. Increased pathology in bleomycin-treated Il13ra1(-/-) mice was due to IL-13Rα1 expression in structural and hematopoietic cells but not due to increased responsiveness to IL-17, IL-4, IL-13, increased IL-13Rα2 or type 1 IL-4R signaling. These data highlight underappreciated protective roles for IL-13Rα1 in lung injury and homeostasis.

Interleukin-33 requires CMRF35-like molecule-1 expression for induction of myeloid cell activation

BACKGROUND

IL-33 is a potent activator of various cells involved in allergic inflammation, including eosinophils and mast cells. Despite its critical role in Th2 disease settings, endogenous molecular mechanisms that may regulate IL-33-induced responses remain to be defined. We have recently shown that eosinophils express CMRF35-like molecule (CLM)-1. Yet, the role of CLM-1 in regulating eosinophil functions is still elusive.

METHODS

CLM-1 and CLM-8 expression and cellular localization were assessed in murine bone marrow-derived and/or peritoneal cells at baseline and following IL-33 stimulation (flow cytometry, western blot). IL-33-induced mediator release and signaling were assessed in wild-type (wt) and Clm1(-/-) cells and mice.

RESULTS

BM-derived eosinophils express high levels of glycosylated CLM-1. IL-33 induced a rapid, specific, concentration- and time-dependent upregulation of CLM-1 in eosinophils (in vitro and in vivo). Clm1(-/-) eosinophils secreted less IL-33-induced mediators than wt eosinophils. CLM-1 co-localized to ST2 following IL-33 stimulation and was required for IL-33-induced NFκB and p38 phosphorylation. Th2 cytokine (e.g., IL-5, IL-13) and chemokine (e.g., eotaxins, CCL2) secretion was markedly attenuated in IL-33-treated Clm1(-/-) mice. Subsequently, IL-33-challenged mice displayed reduced infiltration of mast cells, macrophages, neutrophils, and B cells. Despite the markedly impaired IL-33-induced eotaxin expression in Clm1(-/-) mice, eosinophil accumulation was similar in wt and Clm1(-/-) mice, due to hyperchemotactic responses of Clm1(-/-) eosinophils.

CONCLUSIONS

CLM-1 is a novel regulator of IL-33-induced eosinophil activation. These data contribute to the understanding of endogenous molecular mechanisms regulating IL-33-induced responses and may ultimately lead to receptor-based tools for future therapeutic intervention in IL-33-associated diseases.

CMRF35-like molecule 1 (CLM-1) regulates eosinophil homeostasis by suppressing cellular chemotaxis

Eosinophil accumulation in health and disease is a hallmark characteristic of mucosal immunity and type 2 helper T cell (Th2) inflammation. Eotaxin-induced CCR3 (chemokine (C-C motif) receptor 3) signaling has a critical role in eosinophil chemotactic responses. Nevertheless, the expressions of immunoreceptor tyrosine-based inhibitory motif-bearing receptors such as CMRF35-like molecule-1 (CLM-1) and their ability to govern eosinophil migration are largely unknown. We now report that CLM-1 (but not CLM-8) is highly and distinctly expressed by colonic and adipose tissue eosinophils. Furthermore, Clm1⁻/⁻ mice display elevated baseline tissue eosinophilia. CLM-1 negatively regulated eotaxin-induced eosinophil responses including eosinophil chemotaxis, actin polymerization, calcium influx, and extracellular signal-regulated kinase (ERK)-1/2, but not p38 phosphorylation. Addition of CLM-1 ligand (e.g., phosphatidylserine) rendered wild-type eosinophils hypochemotactic in vitro and blockade of CLM-1/ligand interactions rendered wild-type eosinophils hyperchemotactic in vitro and in vivo in a model of allergic airway disease. Interestingly, suppression of cellular recruitment via CLM-1 was specific to eosinophils and eotaxin, as leukotriene B₄ (LTB₄)- and macrophage inflammatory protein-1α (MIP-1α)-induced eosinophil and neutrophil migration were not negatively regulated by CLM-1. Finally, peripheral blood eosinophils obtained from allergic rhinitis patients displayed elevated CLM-1/CD300f levels. These data highlight CLM-1 as a novel regulator of eosinophil homeostasis and demonstrate that eosinophil accumulation is constantly governed by CLM-1, which negatively regulates eotaxin-induced eosinophil responses.

Regulation of allergic inflammatory responses by inhibitory receptors

An intricate network of activation and inhibitory signals tightly regulates immune responses. To date, multiple activation receptors have been described. These include receptors that mediate cellular functions such as adhesion, chemotaxis, cytokine signalling, mediator release, survival and phagocytosis. In contrast to these activation pathways, an opposing and suppressive receptor system has evolved. These receptors can override the signals elicited by the activation pathways and are broadly termed inhibitory receptors. Inhibitory receptors share unique intracellular signalling motifs and have key roles in various cellular and pathological conditions. Therefore, such receptors are potential targets for future therapeutics. In this review, we will discuss the structure and function of inhibitory receptors. In particular, we will focus on the expression and function of inhibitory receptors on mast cells and eosinophils and illustrate strategies for their inhibition in the settings of allergic inflammation.

Eosinophils: 'new' roles for 'old' cells

Prominent blood and tissue eosinophilia is manifested in a number of inflammatory states, particularly in allergic diseases. Eosinophils are a source of numerous cytokines and growth factors, thus in principle they can display both pro-inflammatory and anti-inflammatory activities as well as immunoregulatory ones. In this review, we will discuss the cross-talk between eosinophils and other cell types that they come in contact with in the inflammatory milieu, such as mast cells, fibroblasts and endothelial cells. 'New' roles for eosinophils in cancer and novel activatory signals will also be described.

IgE-Independent Activation of Human Mast Cells Indicates their Role in the Late Phase Reaction of Allergic Inflammation

Mast cells are tissue dwelling cells that have a clear-cut pathologic role in allergy. Besides that, they participate in several chronic inflammatory conditions, helminitic parasitosis, and in some solid tumor reactions, but also in physiological situations, such as wound healing and innate immunity. Mast cells produce and release various mediators after activation induced by either IgE-dependent or IgE-independent mechanisms. Although much information has been gathered on the immunological (IgE-dependent) mast cell activation both in vivo and in vitro, not much is known about the non-immunological (IgE-independent) activation particularly in human mast cells. Mast cell IgE-independent activation is mediated through Gi3alpha which has been identified in rat mast cells as the pertussis toxin (Ptx)-sensitive heterotrimeric G protein that interacts with cationic secretagogues inducing PLC-independent mast cell exocytosis. Mast cell IgE-independent activation in allergy most likely occurs when mast cells encounter eosinophils, the main inflammatory cells that persist throughout the late and chronic phases of the allergic reaction. This review summarizes the influence of eosinophils on mast cell activation demonstrating that IgE-independent activation has a significant role in pathophysiological processes.

Unilateral duplex horseshoe kidney with ectopic ureterocele

We have reported a case of horseshoe kidney, a common renal fusion anomaly. Because of the 25% incidence of associated genitourinary anomalies, we believe that the diagnosis of horseshoe kidney in pediatric patients should initiate a thorough urologic evaluation, including intravenous urography and real-time sonography.