Participation of complement 3a receptor (C3aR) in the sensitization phase of Th2 mediated allergic contact dermatitis

Proteome Profile of Trigeminal Ganglion in Murine Model of Allergic Contact Dermatitis: Complement 3 Pathway Contributes to Itch and Pain Sensation

Allergic contact dermatitis (ACD) is a common inflammatory dermatosis characterized by persistent itch and pain after topical contact with reactive chemicals. Although it has been long recognized as a type-IV hypersensitivity, its complexity of pathophysiology mechanism makes it still a clinical aporia in treatment. In this study, we aimed to identify crucial proteins involved in the nociceptive sensation of ACD. Based on a chemical-induced ACD murine model, we collected trigeminal ganglions of ACD and control mice for quantitative tandem mass tag (TMT)-labeling proteomic analysis. Immunohistochemistry was further practiced to validate the bioinformatic analysis. A total of 7685 proteins were identified and analyzed. Sixty-four proteins were significantly upregulated, and 75 proteins were downregulated in ACD mice. GO analysis demonstrated that the changed proteins were significantly enriched in terms of immune and peptidase activity in ACD mice. Proteins involved in the complement and coagulation cascades were notably changed in the KEGG enrichment analysis. The upregulation of complement component 3 (C3) in trigeminal satellite cells of ACD mice was further confirmed by immunohistochemistry. ACD upregulated C3 in trigeminal satellite cells. The complement system in sensory ganglion might play an essential role in forming pruritic and nociceptive sensations in ACD.

Altered levels of complement components associated with non-immediate drug hypersensitivity reactions

Nonimmediate drug hypersensitivity reactions (niDHRs) range from mild-type maculopapular exanthema (MPE) to severe type Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) with unentirely clarified pathogenesis. This study sought to explore whether complement components participated in niDHRs. The participants comprised of three groups as follows: MPE (n = 65), SJS/TEN (n = 13, contains 7 SJS, 2 SJS-TEN overlap and 4 TEN), and equal healthy controls (n = 78). Skin pathological changes were confirmed by hematoxylin and eosin staining. The mRNA and protein levels of complement components were assessed. In the MPE group, there were no alterations in complement components at the protein and mRNA levels found except for a decrease in factor H mRNA. In the SJS/TEN group, up-regulated levels of C3aR and C5aR mRNA and down-regulated factor H mRNA levels in blood were noted. A lower plasma protein level of C3, Factor H and a higher level of C3a, C5, C5a, C5b-9, Factor B (p < 0.05) were found in the SJS/TEN group compared with in the control (p < 0.05). In SJS/TEN skin lesions, indirect immunofluorescence assays showed positive specific staining for C5b-9, but not C3. Both C3aR and C5aR were positive staining in the SJS/TEN samples, while staining for C1q, mannose-binding lectin (MBL), Factor B, and Factor H were only weak or negative. The findings reported here are the first to define the expression profiles/extent of the presence of various complement components at the mRNA and protein levels in niDHRs, especially in SJS/TEN. These altered complement components might, at least in part, be integral to the mechanisms underlying the pathogeneses of SJS and TEN.

Complement C3a promotes proliferation, migration and stemness in cutaneous squamous cell carcinoma

Background

Complement C3 has been shown to be highly expressed in cutaneous squamous cell carcinoma (cSCC) tumour tissues and is correlated with tumour cell growth. This study aimed to investigate the mechanism of C3 in cSCC malignant transformation.

Methods

C3 expression was analysed in cSCC cell lines A431, Tca8113, SCC13, HSC‐5 and HSC‐1 and in immortalized HaCaT keratinocytes. Proliferation and migration of cSCC were determined after C3a exposure. Expression of cyclin D1, cyclin E, vascular endothelial growth factor (VEGF), pro‐matrix metalloproteinase 1 (pro‐MMP1), pro‐matrix metalloproteinase 2 (pro‐MMP2), stemness factors, GSK‐3β, and β‐catenin were analyzed. Tumour growth was examined in a murine xenograft model.

Results

C3 expression was much more highly expressed in all cSCC cell lines than in HaCaT cells. C3a treatment significantly promoted cSCC cell proliferation and migration and upregulated cyclin D1, cyclin E, VEGF, pro‐MMP1 and pro‐MMP2 expression, which were impeded by the C3aR antagonist. Moreover, the expression of stemness factors Sox‐2, Nanog, Oct‐4, c‐Myc and CD‐44 was stimulated by C3a and slowed by C3aR disruption. Knockdown of Sox‐2 by siRNA transfection suppressed cell proliferation and migration, constrained VEGF secretion and inhibited pro‐MMP1 and pro‐MMP2 expression. C3a also activated the Wnt and β‐catenin pathway in cSCC cells. Disruption of C3aR expression dampened tumour growth and the expression of Wnt‐1, β‐catenin and Sox‐2 in the xenograft model.

Conclusions

C3a enhanced cell proliferation, migration and stemness in cSCC, and this activity was correlated with activation of the Wnt and β‐catenin pathway.

The Anaphylatoxin C3a Receptor Expression on Human M2 Macrophages Is Down-Regulated by Stimulating the Histamine H4 Receptor and the IL-4 Receptor

The anaphylatoxin C3a triggers inflammation by binding to its specific G-protein-coupled C3a receptor (C3aR). Since the number of C3aR, which is expressed on the cell surface, affects the response to C3a, we investigated the expression levels of C3aR on human M2 macrophages in allergic situations where high levels of the Th2 cytokine IL-4 and histamine are present in a local microenvironment. The histamine H1 receptor (H1R), H2R and the H4R mRNA expressions were induced or up-regulated during the differentiation process of M2 macrophages. The presence of histamine or agonists targeting the H1R, H2R and, in particular, the H4R during in vitro differentiation from monocytes to macrophages modified the M2 phenotype by regulating the macrophage differentiation marker CD68 and CD163 expressions. In -addition, the C3aR expression was also down-regulated by -ST-1006 during this process. Histamine and ST-1006 down-regulated the expression of C3aR with different time kinetics on fully differentiated M2 macrophages. By analysing C3a-induced IL-6 mRNA expression, we observed a diminished response to C3a in ST-1006-treated M2 macrophages when compared to un-treated cells. Expression of C3 was not affected by histamine, whereas IL-4 strongly down-regulated C3aR and C3 expressions. Our data suggests that down-regulation of C3aR expression by mediators present in allergic situations such as IL-4 or histamine has an anti-inflammatory impact by reducing the sensitivity to C3a-induced down-stream signaling, thereby contributing to the regulation of local inflammatory responses in the skin.

Lung-resident eosinophils represent a distinct regulatory eosinophil subset

Increases in eosinophil numbers are associated with infection and allergic diseases, including asthma, but there is also evidence that eosinophils contribute to homeostatic immune processes. In mice, the normal lung contains resident eosinophils (rEos), but their function has not been characterized. Here, we have reported that steady-state pulmonary rEos are IL-5-independent parenchymal Siglec-FintCD62L+CD101lo cells with a ring-shaped nucleus. During house dust mite-induced airway allergy, rEos features remained unchanged, and rEos were accompanied by recruited inflammatory eosinophils (iEos), which were defined as IL-5-dependent peribronchial Siglec-FhiCD62L-CD101hi cells with a segmented nucleus. Gene expression analyses revealed a more regulatory profile for rEos than for iEos, and correspondingly, mice lacking lung rEos showed an increase in Th2 cell responses to inhaled allergens. Such elevation of Th2 responses was linked to the ability of rEos, but not iEos, to inhibit the maturation, and therefore the pro-Th2 function, of allergen-loaded DCs. Finally, we determined that the parenchymal rEos found in nonasthmatic human lungs (Siglec-8+CD62L+IL-3Rlo cells) were phenotypically distinct from the iEos isolated from the sputa of eosinophilic asthmatic patients (Siglec-8+CD62LloIL-3Rhi cells), suggesting that our findings in mice are relevant to humans. In conclusion, our data define lung rEos as a distinct eosinophil subset with key homeostatic functions.

Unique immunomodulatory effects of azelastine on dendritic cells in vitro

Allergic contact dermatitis and atopic dermatitis are among the most common inflammatory skin diseases in western countries, and antigen-presenting cells like dendritic cells (DC) are key players in their pathophysiology. Histamine, an important mediator of allergic reactions, influences DC maturation and cytokine secretion, which led us to investigate the immunomodulatory potential of the well-known histamine H1 receptor antagonists: azelastine, olopatadine, cetirizine, and pyrilamine. Unlike other H1 antihistamines, azelastine decreased lipopolysaccharide-induced tumor necrosis factor α and interleukin-12 secretion from murine bone marrow-derived DC. This effect was independent of histamine receptors H1, H2, or H4 and may be linked to inhibition of the nuclear factor kappa B pathway. Moreover, only azelastine reduced proliferation of allogenic T cells in a mixed leukocyte reaction. We then tested topical application of the H1 antihistamines on mice sensitized against toluene-2,4-diisocyanate, a model of Th2-mediated allergic contact dermatitis. In contrast to the in vitro results, all investigated substances were efficacious in reducing allergic ear swelling. Azelastine has unique effects on dendritic cells and T cell interaction in vitro. However, this did not translate into superior in vivo efficacy for Th2-mediated allergic dermatitis, possibly due to the effects of the antihistamines on other cell types involved in skin inflammation. Future research will have to clarify whether these properties are relevant to in vivo models of allergic inflammation with a different T cell polarization.

The balance between pro- and anti-inflammatory cytokines is crucial in human allergic contact dermatitis pathogenesis: the role of IL-1 family members

The interleukin (IL)-1 family includes 11 members that are important in inflammatory processes. It includes various agonists and two antagonists, IL-1Ra and IL-36Ra. Our aim was to investigate whether the IL-1 family is involved in allergic contact dermatitis (ACD). The expression of IL-1 family members was evaluated by PCR and immunohistochemistry in the positive patch test reaction site (involved skin) and in the uninvolved skin of ACD patients. We also examined these cytokines in an ex vivo model of ACD. The antagonistic activity of IL-36Ra was evaluated by injecting recombinant IL-36Ra in uninvolved skin biopsies of ACD patients. IL-1Ra and IL-36Ra expression was quantified in mononuclear cells of nickel-sensitized patients challenged in vitro with nickel. IL-33 involvement in ACD was investigated by intra-dermal injection of anti-IL-33 in the uninvolved skin of patients ex vivo. Results showed that IL-1β, IL-1Ra, IL-36α, IL-36β, IL-36γ and IL-33 expression, but not IL-36Ra expression, was enhanced in ACD-involved skin. Immunohistochemical analysis and ex vivo skin cultures confirmed these results. Injection of anti-IL-33 in ACD-uninvolved skin inhibited IL-8 expression, whereas IL-36Ra inhibited IL-36α, IL-36β, IL-36γ and IL-8 expression. Nickel induced IL-1Ra expression in lymphocytes of nickel-sensitized patients. Hence, various IL-1 agonists and antagonists may be involved in ACD pathogenesis.

Disruption of the complement anaphylatoxin receptor C5L2 exacerbates inflammation in allergic contact dermatitis

The complement anaphylatoxin C5a is a critical mediator of allergic contact dermatitis, bridging essential aspects of innate and adaptive immunity. This anaphylatoxin functions by interacting with two 7-transmembrane segment receptors, the C5aR and C5L2. The C5aR is a classical G protein coupled receptor, whereas C5L2 is deficient in coupling to G proteins because of variations in the sequence. Our previous work in human neutrophils revealed a unique role for C5L2 in negatively modulating anaphylatoxin receptor mediated cellular activation through interactions with β-arrestin. When C5L2 is deficient, C5aR-mediated β-arrestin signaling is greatly enhanced. The work described in this study was undertaken first to determine the effect of C5L2 deficiency in a murine model of contact sensitivity, and second to determine whether the resultant exacerbation of inflammatory parameters reflects a negative modulatory function of C5L2 on the C5aR. First, we find dramatic increases in inflammation in C5L2(-/-) animals compared with wild type mice. Second, these increases are completely reversed following administration of mAb against the C5aR. Thus, in allergic contact sensitivity, as in isolated human neutrophils, C5L2 functions to suppress C5a-C5aR-mediated responses, further underscoring its role as a negative regulator of anaphylatoxin activity.

Complement component 3C3 and C3a receptor are required in chitin-dependent allergic sensitization to Aspergillus fumigatus but dispensable in chitin-induced innate allergic inflammation

Levels of the anaphylatoxin C3a are increased in patients with asthma compared with those in nonasthmatics and increase further still during asthma exacerbations. However, the role of C3a during sensitization to allergen is poorly understood. Sensitization to fungal allergens, such as Aspergillus fumigatus, is a strong risk factor for the development of asthma. Exposure to chitin, a structural polysaccharide of the fungal cell wall, induces innate allergic inflammation and may promote sensitization to fungal allergens. Here, we found that coincubation of chitin with serum or intratracheal administration of chitin in mice resulted in the generation of C3a. We established a model of chitin-dependent sensitization to soluble Aspergillus antigens to test the contribution of complement to these events. C3^−/− and C3aR^−/− mice were protected from chitin-dependent sensitization to Aspergillus and had reduced lung eosinophilia and type 2 cytokines and serum IgE. In contrast, complement-deficient mice were not protected against chitin-induced innate allergic inflammation. In sensitized mice, plasmacytoid dendritic cells from complement-deficient animals acquired a tolerogenic profile associated with enhanced regulatory T cell responses and suppressed Th2 and Th17 responses specific for Aspergillus. Thus, chitin induces the generation of C3a in the lung, and chitin-dependent allergic sensitization to Aspergillus requires C3aR signaling, which suppresses regulatory dendritic cells and T cells and induces allergy-promoting T cells.

Asthma is one of the fastest growing chronic illnesses worldwide. Chitin, a ubiquitous polymer in our environment and a key component in the cell wall of fungal spores and the exoskeletons of insects, parasites, and crustaceans, triggers innate allergic inflammation. However, there is little understanding of how chitin is initially recognized by mammals and how early recognition of chitin affects sensitization to environmental allergens and development of allergic asthma. The complement system is evolutionarily one of the oldest facets of the early or innate warning systems in mammals. We studied whether and how complement components influence the recognition of chitin and shape the downstream sensitization toward fungal allergens. We show here that complement recognition of chitin plays a critical role in shaping the behavior of dendritic cells, which in turn regulate the function of T cells that mediate allergic responses to fungi.