Role of CCL7 in Type I Hypersensitivity Reactions in Murine Experimental Allergic Conjunctivitis

Molecules that are necessary for ocular hypersensitivity reactions include the receptors CCR1 and CCR3; CCL7 is a ligand for these receptors. Therefore, we explored the role of CCL7 in mast cell activity and motility in vitro and investigated the requirement for CCL7 in a murine model of IgE-mediated allergic conjunctivitis. For mast cells treated with IgE and Ag, the presence of CCL7 synergistically enhanced degranulation and calcium influx. CCL7 also induced chemotaxis in mast cells. CCL7-deficient bone marrow-derived mast cells showed decreased degranulation following IgE and Ag treatment compared with wild-type bone marrow-derived mast cells, but there was no difference in degranulation when cells were activated via an IgE-independent pathway. In vivo, CCL7 was upregulated in conjunctival tissue during an OVA-induced allergic response. Notably, the early-phase clinical symptoms in the conjunctiva after OVA challenge were significantly higher in OVA-sensitized wild-type mice than in control challenged wild-type mice; the increase was suppressed in CCL7-deficient mice. In the OVA-induced allergic response, the numbers of conjunctival mast cells were lower in CCL7-deficient mice than in wild-type mice. Our results demonstrate that CCL7 is required for maximal OVA-induced ocular anaphylaxis, mast cell recruitment in vivo, and maximal FcεRI-mediated mast cell activation in vitro. A better understanding of the role of CCL7 in mediating ocular hypersensitivity reactions will provide insights into mast cell function and novel treatments for allergic ocular diseases.

New twists to an old story: novel concepts in the pathogenesis of allergic eye disease

The prevalence of allergy is rising globally at a very significant rate, which is currently at 20-40% of individuals in westernized nations. In the eye, allergic conditions can take on the acute form such as in seasonal and perennial allergic conjunctivitis, or a more severe and debilitating chronic form such as in vernal and atopic keratoconjunctivitis. Indeed, some key aspects of allergic eye disease pathophysiology are understood, such as the role of mast cells in the acute allergic reaction, and the contribution of eosinophils in late-onset and chronic allergy. However, recent developments in animal models and clinical studies have uncovered new and important roles for previously underappreciated players, including chemokine receptors on ocular surface dendritic cells such as CCR7, the contribution of conjunctival epithelium to immunity, histamine and leukotriene receptors on conjunctival goblet cells and a role for mast cells in late-onset manifestations. Furthermore, recent work in animal models has delineated the contribution of IL-4 in the increased incidence of corneal graft rejection in hosts with allergic conjunctivitis. Recent studies such as these mean that conventional paradigms and concepts should be revisited. The aim of this review is to highlight some of the most recent advances and insights on newly appreciated players in the pathogenesis of allergic eye disease.

CCR2 Antagonists for the Treatment of Diseases Associated with Inflammation

The CCR2 and MCP-1 pathway has become one of the most-studied chemokine systems for therapeutic use in inflammatory diseases and conditions. It plays a pivotal role in inflammatory diseases, especially those that are characterized by monocyte-rich infiltration. This chapter reviews the biology of CCR2 and MCP-1, and their roles in diseases and conditions related to inflammation such as rheumatoid arthritis, multiple sclerosis, asthma, obesity, type 2 diabetes, atherosclerosis, nephropathy, cancer, pulmonary fibrosis and pain. Intense drug-discovery efforts over the past 15 years have generated a large number of CCR2 antagonists in diverse structural classes. Mutagenesis studies have elucidated important residues on CCR2 that interact with many classes of these CCR2 antagonists. To facilitate understanding of CCR2 antagonist SAR, a simple pharmacophore model is used to summarize the large number of diverse chemical structures. The majority of published compounds are classified based on their central core structures using this model. Key SAR points in the published literature are briefly discussed for most of the series. Lead compounds in each chemical series are highlighted where information is available. The challenges in drug discovery and development of CCR2 antagonists are briefly discussed. Clinical candidates in various diseases in the public domain are summarized with a brief discussion about the clinical challenges.

Evidence that formation of vimentin mitogen-activated protein kinase (MAPK) complex mediates mast cell activation following FcεRI/CC chemokine receptor 1 cross-talk

Accumulating evidence points to cross-talk between FcεRI and CC chemokine receptor (CCR)-mediated signaling pathways in mast cells. Here, we propose that vimentin, a protein comprising type III intermediate filament, participates in such cross-talk for CCL2/monocyte chemotactic protein 1 (MCP-1) production in mast cells, which is a mechanism for allergic inflammation. Co-stimulation via FcεRI, using IgE/antigen, and CCR1, using recombinant CCL3/macrophage inflammatory protein-1α (MIP-1α), increased expression of phosphorylated, disassembled, and soluble vimentin in rat basophilic leukemia (RBL)-2H3 cells expressing human CCR1 (RBL-CCR1 cells) and bone marrow-derived murine mast cells, both models of mucosal type mast cells. Furthermore, co-stimulation enhanced production of CCL2 as well as phosphorylation of MAPK. Treating the cells with p38 MAPK inhibitor SB203580, but not with MEK inhibitor PD98058, reduced CCL2 production, suggesting that p38 MAPK, but not ERK1/2, plays a critical role in the chemokine production. Immunoprecipitation analysis showed that vimentin interacts with phosphorylated ERK1/2 and p38 MAPKs in the co-simulated cells. Preventing disassembly of the vimentin by aggregating vimentin filaments using β,β'-iminodipropionitrile reduced the interaction of vimentin with phosphorylated MAPKs as well as CCL2 production in the cells. Taken together, disassembled vimentin interacting with phosphorylated p38 MAPK could mediate CCL2 production in mast cells upon FcεRI and CCR1 activation.

Identification of genes and proteins specifically regulated by costimulation of mast cell Fcε Receptor I and chemokine receptor 1

Mast cell function is a critical component of allergic reactions. Mast cell responses mediated by the high-affinity immunoglobulin E receptor FcεRI can be enhanced by co-activation of additional receptors such as CC chemokine receptor 1 (CCR1). To examine the downstream effects of FcεRI-CCR1 costimulation, rat basophilic leukemia cells stably transfected with CCR1 (RBL-CCR1 cells) were sensitized and activated with antigen and/or the CCR1 ligand CC chemokine ligand (CCL) 3. Gene and protein expression were determined at 3h and 24h post-activation, respectively, using GeneChip and Luminex bead assays. Gene microarray analysis demonstrated that 32 genes were differentially regulated in response to costimulation, as opposed to stimulation with antigen or CCL3 alone. The genes most significantly up-regulated by FcεRI-CCR1 costimulation were Ccl7, Rgs1, Emp1 and RT1-S3. CCL7 protein was also expressed at higher levels 24h after dual receptor activation, although RGS1, EMP1 and RT1-S3 were not. Of the panel of chemokines and cytokines tested, only CCL2, CCL7 and interleukin (IL)-6 were expressed at higher levels following costimulation. IL-6 expression was seen only after FcεRI-CCR1 costimulation, although the amount expressed was very low. CCL7, CCL2 and IL-6 might play roles in mast cell regulation of late-phase allergic responses.

CCR1 expression and signal transduction by murine BMMC results in secretion of TNF-alpha, TGFbeta-1 and IL-6

Chemokine receptors (CCRs) are important co-stimulatory molecules found on many blood cells and associated with various diseases. The expression and function of CCRs on mast cells has been quite controversial. In this study, we report for the first time that murine bone marrow-derived mast cells (BMMC) express messenger RNA and protein for CCR1. BMMC cultured in the presence of murine recombinant stem cell factor and murine IL-3 expressed CCR1 after 5-6 weeks. We also report for the first time that mBMMC(CCR1+) cells endogenously express neurokinin receptor-1 and intercellular adhesion molecule-1. To examine the activity of CCR1 on these BMMC, we simultaneously stimulated two receptors: CCR1 by its ligand macrophage inflammatory protein-1alpha and the IgE receptor FcepsilonRI by antigen cross-linking. We found that co-stimulation enhanced BMMC degranulation compared with FcepsilonRI stimulation alone, as assessed by beta-hexosaminidase activity (85 versus 54%, P < 0.0001) and Ca(2+) influx (223 versus 183 nM, P < 0.05). We also observed significant increases in mast cell secretion of key growth factors, cytokines and chemokine mediators upon CCR1-FcepsilonRI co-stimulation. These factors include transforming growth factor beta-1, tumor necrosis factor-alpha and the cytokine IL-6. Taken together, our data indicate that CCR1 plays a key role in BMMC function. These findings contribute to our understanding of mechanisms for immune cell trafficking during inflammation.