Enhanced contact hypersensitivity in human monocyte chemoattractant protein-1 transgenic mouse

MR1 deficiency enhances IL-17-mediated allergic contact dermatitis

Major histocompatibility complex (MHC) class Ib molecules present antigens to subsets of T cells primarily involved in host defense against pathogenic microbes and influence the development of immune-mediated diseases. The MHC class Ib molecule MHC-related protein 1 (MR1) functions as a platform to select MR1-restricted T cells, including mucosal-associated invariant T (MAIT) cells in the thymus, and presents ligands to them in the periphery. MAIT cells constitute an innate-like T-cell subset that recognizes microbial vitamin B₂ metabolites and plays a defensive role against microbes. In this study, we investigated the function of MR1 in allergic contact dermatitis (ACD) by examining wild-type (WT) and MR1-deficient (MR1^-/-) mice in which ACD was induced with 2,4-dinitrofluorobenzene (DNFB). MR1^-/- mice exhibited exaggerated ACD lesions compared with WT mice. More neutrophils were recruited in the lesions in MR1^-/- mice than in WT mice. WT mice contained fewer MAIT cells in their skin lesions following elicitation with DNFB, and MR1^-/- mice lacking MAIT cells exhibited a significant increase in IL-17-producing αβ and γδ T cells in the skin. Collectively, MR1^-/- mice displayed exacerbated ACD from an early phase with an enhanced type 3 immune response, although the precise mechanism of this enhancement remains elusive.

Critical Players and Therapeutic Targets in Chronic Itch

Chronic itch is one of the most prominent clinical characteristics of diverse systematic diseases. It is a devastating sensation in pathological diseases. Despite its importance, there are no FDA-labelled drugs specifically geared toward chronic itch. The associated complex pathogenesis and diverse causes escalate chronic itch to being one of the top challenges in healthcare. Humanized antibodies against IL-13, IL-4, and IL-31 proved effective in treatment of itch-associated atopic dermatitis but remain to be validated in chronic itch. There are still no satisfactory anti-itch therapeutics available toward itch-related neuropeptides including GRP, BNP, SST, CGRP, and SP. The newly identified potential itch targets including OSM, NMB, glutamate, periostin, and Serpin E1 have opened new avenues for therapeutic development. Proof-of-principle studies have been successfully performed on antagonists against these proteins and their receptors in itch treatment in animal models. Their translational interventions in humans need to be evaluated. It is of great importance to summarize and compare the newly emerging knowledge on chronic itch and its pathways to promote the development of novel anti-itch therapeutics. The goal of this review is to analyze the different physiologies and pathophysiologies of itch mediators, whilst assessing their suitability as new targets and discussing future therapeutic development.

Immune-Regulatory and Molecular Effects of Antidepressants on the Inflamed Human Keratinocyte HaCaT Cell Line

Allergic contact dermatitis (ACD) is a T cell-mediated type of skin inflammation resulting from contact hypersensitivity (CHS) to antigens. There is strong comorbidity between ACD and major depression. Keratinocytes release immunomodulatory mediators including pro-inflammatory cytokines and chemokines, which modulate skin inflammation and are crucial cell type for the development of CHS. Our previous studies showed that fluoxetine and desipramine were effective in suppressing CHS in different mouse strains. However, the immune and molecular mechanisms underlying this effect remain to be explored. The aim of the current study was to determine the immune and molecular mechanisms of action of antidepressant drugs engaged in the inhibition of CHS response in the stimulated keratinocyte HaCaT cell line. The results show that LPS, TNF-α/IFN-γ, and DNFB stimulate HaCaT cells to produce large amounts of pro-inflammatory factors including IL-1β, IL-6, CCL2, and CXCL8. HaCaT stimulation was associated with increased expression of ICAM-1, a cell adhesion molecule, and decreased expression of E-cadherin. Imipramine, desipramine, and fluoxetine suppress the production of IL-1β, CCL2, as well as the expression of ICAM-1. LPS and TNF-α/IFN-γ activate p-38 kinase, but antidepressants do not regulate this pathway. LPS decreases E-cadherin protein expression and fluoxetine normalizes these effects. In summary, the antidepressant drugs examined in this study attenuate the stimulated secretion of pro-inflammatory cytokines, chemokines, and modulate adhesion molecule expression by the HaCaT cell line. Therefore, antidepressants may have some clinical efficacy in patients with ACD and patients with comorbid depression and contact allergy.

Itch: A Paradigm of Neuroimmune Crosstalk

Although the medical definition of itch has been in existence for 360 years, only in the last 20 years have we begun to understand the basic mechanisms that underlie this unique sensation. Therapeutics that specifically target chronic itch as a pathologic entity are currently still not available. Recent seminal advances in itch circuitry within the nervous system have intersected with discoveries in immunology in unexpected ways to rapidly inform emerging treatment strategies. The current review aims to introduce these basic concepts in itch biology and highlight how distinct immunologic pathways integrate with recently identified itch-sensory circuits in the nervous system to inform a major new paradigm of neuroimmunology and therapeutic development for chronic itch.

MCP-1 Priming Enhanced the Therapeutic Effects of Human Mesenchymal Stromal Cells on Contact Hypersensitivity Mice by Activating the COX2-PGE2/STAT3 Pathway

Mesenchymal stromal cells (MSCs) have become a promising treatment for inflammation-related diseases, and their therapeutic efficacy mainly depends on crosstalk between MSCs and inflammation. However, methods to improve the immunosuppressive efficiency of MSCs in different diseases still need to be developed. In this study, we investigated whether preconditioning MSCs with a disease-related inflammatory cytokine could increase their immunosuppressive properties and improve therapeutic efficacy. In a contact hypersensitivity (CHS) mouse model, inflammatory profile screening revealed that among all tested cytokines, monocyte chemotactic protein-1 (MCP-1) exhibited the most significantly increased level in the local microenvironment. As expected, MSCs preconditioned with MCP-1 (P-MSCs) exhibited an enhanced ability to downregulate proinflammatory cytokine secretion, induce regulatory T cells, inhibit T cell proliferation, and polarize M2-type macrophages. In vivo experiments showed that P-MSCs alleviated ear swelling and local proinflammatory cytokine production more effectively than control MSCs. Mechanistically, MCP-1 could significantly activate the signal transducer and activator of transcription 3 (STAT3) signaling pathway and induce the expression of cyclooxygenase-2 (COX2) and prostaglandin E2 (PGE2) in MSCs. STAT3 inhibitor reversed the MCP-1-mediated enhancing of their immunosuppressive ability. Collectively, our findings demonstrate that CHS-related MCP-1 preconditioning enhanced the immunomodulatory effects of MSCs and improved their therapeutic efficacy in CHS. Enhancing the immunosuppressive efficacy of MSCs by preconditioning with certain disease-related inflammatory cytokines may provide a new strategy for MSC-based therapies for inflammatory diseases.

CCL2/CCR2 signaling elicits itch- and pain-like behavior in a murine model of allergic contact dermatitis

Spontaneous itch and pain are the most common symptoms in various skin diseases, including allergic contact dermatitis (ACD). The chemokine (C-C motif) ligand 2 (CCL2, also referred to as monocyte chemoattractant protein 1 (MCP-1)) and its receptor CCR2 are involved in the pathophysiology of ACD, but little is known of the role of CCL2/CCR2 for the itch- and pain-behaviors accompanying the murine model of this disorder, termed contact hypersensitivity (CHS). C57BL/6 mice previously sensitized to the hapten, squaric acid dibutyl ester, applied to the abdomen were subsequently challenged twice with the hapten delivered to either the cheek or to the hairy skin of the hind paw resulting in CHS at that site. By 24 h after the 2nd challenge to the hind paw CCL2 and CCR2 mRNA, protein, and signaling activity were upregulated in the dorsal root ganglion (DRG). Calcium imaging and whole-cell current-clamp recordings revealed that CCL2 directly acted on its neuronal receptor, CCR2 to activate a subset of small-diameter, nociceptive-like DRG neurons retrogradely labeled from the CHS site. Intradermal injection of CCL2 into the site of CHS on the cheek evoked site-directed itch- and pain-like behaviors which could be attenuated by prior delivery of an antagonist of CCR2. In contrast, CCL2 failed to elicit either type of behavior in control mice. Results are consistent with the hypothesis that CHS upregulates CCL2/CCR2 signaling in a subpopulation of cutaneous small diameter DRG neurons and that CCL2 can activate these neurons through neuronal CCR2 to elicit itch- and pain-behavior. Targeting the CCL2/CCR2 signaling might be beneficial for the treatment of the itch and pain sensations accompanying ACD in humans.

CCR2 plays a critical role in dendritic cell maturation: possible role of CCL2 and NF-kappa B

We postulated that CCR2-driven activation of the transcription factor NF-kappaB plays a critical role in dendritic cell (DC) maturation (e.g., migration, costimulation, and IL-12p70 production), necessary for the generation of protective immune responses against the intracellular pathogen Leishmania major. Supporting this notion, we found that CCR2, its ligand CCL2, and NF-kappaB were required for CCL19 production and adequate Langerhans cell (LC) migration both ex vivo and in vivo. Furthermore, a role for CCR2 in upregulating costimulatory molecules was indicated by the reduced expression of CD80, CD86, and CD40 in Ccr2(-/-) bone marrow-derived dendritic cells (BMDCs) compared with wild-type (WT) BMDCs. Four lines of evidence suggested that CCR2 plays a critical role in the induction of protective immunity against L. major by regulating IL-12p70 production and migration of DC populations such as LCs. First, compared with WT, Ccr2(-/-) lymph node cells, splenocytes, BMDCs, and LCs produced lower levels of IL-12p70 following stimulation with LPS/IFN-gamma or L. major. Second, a reduced number of LCs carried L. major from the skin to the draining lymph nodes in Ccr2(-/-) mice compared with WT mice. Third, early treatment with exogenous IL-12 reversed the susceptibility to L. major infection in Ccr2(-/-) mice. Finally, disruption of IL-12p70 in radioresistant cells, such as LCs, but not in BMDCs resulted in the inability to mount a fully protective immune response in bone marrow chimeric mice. Collectively, our data point to an important role for CCR2-driven activation of NF-kappaB in the regulation of DC/LC maturation processes that regulate protective immunity against intracellular pathogens.

The histamine H4 receptor mediates inflammation and pruritus in Th2-dependent dermal inflammation

The role of histamine H(4) receptor (H(4)R) was investigated in a T-helper type 2 (Th2)-cell-mediated mouse skin inflammation model that mimics several of the features of atopic dermatitis. Treatment with two specific H(4)R antagonists before challenge with FITC led to a significant reduction in ear edema, inflammation, mast cell, and eosinophil infiltration. This was accompanied by a reduction in the levels of several cytokines and chemokines in the ear tissue. Upon ex vivo antigen stimulation of lymph nodes, H(4)R antagonism reduced lymphocyte proliferation and IL-4, IL-5, and IL-17 levels. One explanation for this finding is that lymph nodes from animals dosed with the H(4)R antagonist, JNJ 7777120, contained a lower number of FITC-positive dendritic cells. The effect of H(4)R antagonism on dendritic cell migration in vivo may be an indirect result of the reduction in tissue cytokines and chemokines or a direct effect on chemotaxis. In addition to anti-inflammatory effects, JNJ 7777120 also significantly inhibited the pruritus shown in the model. Therefore, the dual effects of H(4)R antagonists on pruritus and Th2-cell-mediated inflammation point to their therapeutic potential for the treatment of Th2-mediated skin disorders, including atopic dermatitis.

Auf1/Hnrnpd-deficient mice develop pruritic inflammatory skin disease

Mice lacking heterogenous nuclear ribonuclear protein D (Hnrnpd), also known as Auf1, a regulator of inflammatory cytokine mRNA stability, develop chronic dermatitis with age that is characterized by pruritus and excoriations. Histological analysis showed marked epidermal acanthosis and spongiosis, neovascularization, and elevated number of inflammatory cells, including T cells, macrophages, neutrophils, mast cells, and eosinophils. Hnrnpd-deficient (Hnrnpd(tm1Rjsc)) mice with dermatitis display elevated serum IgE levels. Lesions in Hnrnpd(tm1Rjsc) mice were associated with a shift towards a Th(2) immune environment. Evaluation of T-cell-mediated skin inflammation by assaying contact hypersensitivity indicated an increased response in Hnrnpd(tm1Rjsc) mice. T cells and macrophages from Hnrnpd(tm1Rjsc) mice demonstrate a number of abnormalities associated with dermatitis, including increased IL2, tumor-necrosis factor-alpha (TNFalpha), and IL1beta production. Finally, many features of spontaneous dermatitis could be recapitulated in experimentally induced lesions by subcutaneous injection of CCL27 and TNF in unaffected Hnrnpd(tm1Rjsc) mice. Collectively, these data highlight the importance of HNRNPD and proper regulation of mRNA stability in the intricate processes of leukocyte recruitment and inflammatory activation within the skin.

MMP19 is essential for T cell development and T cell-mediated cutaneous immune responses

Matrix metalloproteinase-19 (MMP19) affects cell proliferation, adhesion, and migration in vitro but its physiological role in vivo is poorly understood. To determine the function of MMP19, we generated mice deficient for MMP19 by disrupting the catalytic domain of mmp19 gene. Although MMP19-deficient mice do not show overt developmental and morphological abnormalities they display a distinct physiological phenotype. In a model of contact hypersensitivity (CHS) MMP19-deficient mice showed impaired T cell-mediated immune reaction that was characterized by limited influx of inflammatory cells, low proliferation of keratinocytes, and reduced number of activated CD8(+) T cells in draining lymph nodes. In the inflamed tissue, the low number of CD8(+) T cells in MMP19-deficient mice correlated with low amounts of proinflammatory cytokines, especially lymphotactin and interferon-inducible T cell alpha chemoattractant (I-TAC). Further analyses showed that T cell populations in the blood of immature, unsensitized mice were diminished and that this alteration originated from an altered maturation of thymocytes. In the thymus, thymocytes exhibited low proliferation rates and the number of CD4(+)CD8(+) double-positive cells was remarkably augmented. Based on the phenotype of MMP19-deficient mice we propose that MMP19 is an important factor in cutaneous immune responses and influences the development of T cells.

Downregulation of monocyte chemoattractant protein-1 involving short interfering RNA attenuates hapten-induced contact hypersensitivity

Contact hypersensitivity (CHS) is a common skin disease, presenting clinically as allergic contact dermatitis. At inflammatory sites in a typical CHS model in the mouse ear, elevated expression of monocyte chemoattractant protein-1 (MCP-1) has been reported. MCP-1 is a potent chemotactic factor for many types of leukocytes including monocytes/macrophages and T cells. In this study, we aimed at developing a therapy for CHS involving RNA interference targeting MCP-1. A short interfering RNA (siRNA) to mouse MCP-1 successfully inhibited the secretion of MCP-1 by a fibroblastic cell line, L929, and RAW 264.7 cells derived from macrophages, and strikingly suppressed ear swelling in a CHS model. The siRNA systemically administered inhibited the infiltration of both monocytes/macrophages and T cells in the CHS model. Atelocollagen was used in this therapy as a delivery reagent for siRNA into the animal body. Atelocollagen facilitated the incorporation of the siRNA into macrophages/monocytes and fibroblasts, which vigorously secrete MCP-1 protein at inflammatory sites in CHS. This therapy had no adverse effects such as induction of interferon, or liver or renal damage. Our data indicate that the systemic delivery of siRNA targeting MCP-1 is a potent therapeutic strategy for CHS treatment.

Genetic aspects of immune-mediated adverse drug effects

Adverse drug effects (ADEs) are of great importance in medicine and account for up to 5% of all hospital admissions. ADEs can arise from several mechanisms and a wide range of drugs can cause immune-mediated ADEs (IMADEs). For a drug to elicit an IMADE, it must be both immunogenic (that is, able to sensitize the immune system) and antigenic (that is, able to evoke a response from a sensitized immune system). Unlike protein therapeutics, small-molecule drugs (or xenobiotics) are usually neither immunogenic nor antigenic. IMADEs are therefore the result of complex interactions between drug-metabolizing enzymes, immune sensitization and immune effectors. The genetic aspects of this interplay are discussed in this review.

Impaired lung dendritic cell activation in CCR2 knockout mice

Dendritic cell (DC) recruitment is a hallmark event in antigen (Ag)-challenged lungs. We previously reported models for analyzing DC migration and activation in the lung after Th1- or Th2-eliciting pathogen Ag-bead challenge. To determine the role of chemokines in DC mobilization, we applied this analysis to CCR1, CCR2, CCR5, and CCR6 chemokine receptor knockout mice. Both Mycobacteria bovis protein Ags and helminthic, Schistosoma mansoni egg Ags elicited multiple chemokines, including CCR1, CCR2, CCR5, and to a lesser extent CCR6 ligands. DCs from wild-type lungs expressed transcripts for chemokine receptors, CCR1, CCR2, CCR5, and CXCR4. In all knockout strains, CD11c+ cells were recruited to Ag-beads likely because of receptor redundancy. However, DCs in CCR2-/- mice had significantly decreased MHCII and CD40 expression. This was associated with abrogated cytokine production in draining lymph node cultures. Analysis of local innate inflammation revealed a 50% reduction in macrophage recruitment in CCR2-/- mice. Bone marrow chimeras of mixed CCR2+/+ green fluorescent protein transgenic and CCR2-/- green fluorescent protein-negative cells confirmed the DC maturation defect was only among the latter population. In conclusion, CCR2 knockout confers an intrinsic DC activation defect and CCR2 ligands likely promote the local activation/maturation of inflammatory DCs.

Immune Sensitization in the Skin Is Enhanced by Antigen-Independent Effects of IgE

Contact sensitivity responses require both effective immune sensitization following cutaneous exposure to chemical haptens and antigen-specific elicitation of inflammation upon subsequent hapten challenge. We report that antigen-independent effects of IgE antibodies can promote immune sensitization to haptens in the skin. Contact sensitivity was markedly impaired in IgE(-/-) mice but was restored by either transfer of sensitized cells from wild-type mice or administration of hapten-irrelevant IgE before sensitization. Moreover, IgE(-/-) mice exhibited impairment in the reduction of dendritic cell numbers in the epidermis after hapten exposure. Monomeric IgE has been reported to influence mast cell function. We observed diminished contact sensitivity in mice lacking FcepsilonRI or mast cells, and mRNA for several mast cell-associated genes was reduced in IgE(-/-) versus wild-type skin after hapten exposure. We speculate that levels of IgE normally present in mice favor immune sensitization via antigen-independent but FcepsilonRI-dependent effects on mast cells.

Augmented expression of tumour necrosis factor-alpha induced by lipopolysaccharide in spleen of human monocyte chemoattractant protein-1 transgenic mouse enhances the lipopolysaccharide sensitivity of the marginal zone macrophages

Monocyte chemoattractant protein-1 (MCP-1) is a protective cytokine in murine endotoxaemia induced by lipopolysaccharide (LPS). In this study, LPS-induced pathophysiology in the human (h) MCP-1 transgenic mouse (Tgm) line was investigated. The hMCP-1 Tgm showed a marked increase in the mortality and weight loss following LPS administration. In the Tgm spleens, disappearance of marginal zone macrophages (MZMphi) and dendritic cells (DC) was induced by a smaller amount of LPS than that required for the disappearance in non-transgenic littermates. A significant number of apoptotic cells were seen in these areas. Furthermore, expressions of tumour necrosis factor-alpha (TNF-alpha), interleukin-1alpha (IL-1alpha), and IL-6 mRNA were enhanced and sustained in the LPS-treated Tgm. Neutralization of TNF-alpha considerably depressed the LPS-sensitivity of Tgm. These findings demonstrate that the continuous and systemic presence of MCP-1 is no more protective toward endotoxaemia and suggest that the high sensitivity of the MZMphi and DC to LPS is attributed to the enhanced TNF-alpha production in the hMCP-1 Tgm.