Peptidoglycan-induced T helper 2 immune response in mice involves interleukin-10 secretion from Langerhans cells

Interactions between skin-resident dendritic and Langerhans cells and pain-sensing neurons

Various immune cells in the skin contribute to its function as a first line of defense against infection and disease, and the skin's dense innervation by pain-sensing sensory neurons protects the host against injury or damage signals. Dendritic cells (DCs) are a heterogeneous population of cells that link the innate immune response to the adaptive response by capturing, processing, and presenting antigens to promote T-cell differentiation and activation. DCs are abundant across peripheral tissues, including the skin, where they are found in the dermis and epidermis. Langerhans cells (LCs) are a DC subset located only in the epidermis; both populations of cells can migrate to lymph nodes to contribute to broad immune responses. Dermal DCs and LCs are found in close apposition with sensory nerve fibers in the skin and express neurotransmitter receptors, allowing them to communicate directly with the peripheral nervous system. Thus, neuroimmune signaling between DCs and/or LCs and sensory neurons can modulate physiologic and pathophysiologic pathways, including immune cell regulation, host defense, allergic response, homeostasis, and wound repair. Here, we summarize the latest discoveries on DC- and LC-neuron interaction with neurons while providing an overview of gaps and areas not previously explored. Understanding the interactions between these 2 defence systems may provide key insight into developing therapeutic targets for treating diseases such as psoriasis, neuropathic pain, and lupus.

Peptidoglycan-based immunomodulation

Peptidoglycan (PGN) is a unique component in the cytoderm of prokaryotes which can be recognized by different pathogen-associated molecular patterns (PAMPs) in eukaryotes, followed by a cascade of immune responses via different pathways. This review outlined the basic structure of PGN, its immunologic functions. The immunomodulation pathways mediated by PGN were elaborated. PGN induces specific immunity through stimulating different cytokine release and Th1/Th2-dominated immune responses during humoral/cellular immune response. The nonspecific immunity activation by PGN involves immunomodulation by different pattern recognition receptors (PRRs) including PGN recognition proteins (PGRPs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), Toll-like receptors (TLRs), and C-type lectin receptors (CLRs). The sources and classification of PGRPs were summarized. In view of the stimulating activities of PGN and its monomers, the potential application of PGN as vaccine or adjuvant was prospected. This review provides systematic information on PGN functionalities from the point of immunoregulation, which might be useful in the deep exploitation of PGN.Key points. The immunological functions of PGN were illustrated. Cellular and humoral immunomodulation by PGN were outlined. The use of PGN as vaccine or adjuvant was prospected.

Alpha synuclein, the culprit in Parkinson disease, is required for normal immune function

Alpha-synuclein (αS) is causally involved in the development of Parkinson disease (PD); however, its role in normal vertebrate physiology has remained unknown. Recent studies demonstrate that αS is induced by noroviral infection in the enteric nervous system of children and protects mice against lethal neurotropic viral infection. Additionally, αS is a potent chemotactic activator of phagocytes. In this report, using both wild-type and αS knockout mice, we show that αS is a critical mediator of inflammatory and immune responses. αS is required for the development of a normal inflammatory response to bacterial peptidoglycan introduced into the peritoneal cavity as well as antigen-specific and T cell responses following intraperitoneal immunization. Furthermore, we show that neural cells are the sources of αS required for immune competence. Our report supports the hypothesis that αS accumulates within the nervous system of PD individuals because of an inflammatory/immune response.

Effects of Josamycin on Scratching Behavior in NC/Nga Mice with Atopic Dermatitis-Like Skin Lesions

Our previous study showed that chronic skin colonization by Staphylococcus aureus exacerbated atopic dermatitis (AD) and that control of such skin colonization using antibiotic ointment might relieve AD-related skin inflammation. However, the role of S. aureus colonization in the pruritus accompanying AD was not elucidated. The aim of the present study was to evaluate the effect of topically applied josamycin, a macrolide antibiotic, on the scratching behavior of NC/Nga mice with AD-like skin lesions. Josamycin (0.1%) was topically administered to NC/Nga mice with AD-like skin lesions induced by a mite antigen, Dermatophagoides farinae extract, and the therapeutic effects of josamycin were assessed by measurement of the skin severity score, S. aureus colonization, scratching count, and interleukin (IL)-31 mRNA expression in the skin lesions. Topical treatment with josamycin ointment significantly suppressed the increase of the skin severity score in NC/Nga mice. This suppressive effect was associated with decreases in the S. aureus count on the lesioned skin, scratching behavior of mice and IL-31 mRNA expression in the lesions. The present results show that the severity of AD-like skin inflammation in NC/Nga mice is correlated with the level of S. aureus colonization and subsequent IL-31 production in the skin. Therefore, topical application of josamycin to AD lesions colonized by S. aureus would be beneficial for control of AD by eliminating superficially located S. aureus and by suppressing the IL-31-induced scratching behavior.

Gut-Skin Axis: Current Knowledge of the Interrelationship between Microbial Dysbiosis and Skin Conditions

The microbiome plays an important role in a wide variety of skin disorders. Not only is the skin microbiome altered, but also surprisingly many skin diseases are accompanied by an altered gut microbiome. The microbiome is a key regulator for the immune system, as it aims to maintain homeostasis by communicating with tissues and organs in a bidirectional manner. Hence, dysbiosis in the skin and/or gut microbiome is associated with an altered immune response, promoting the development of skin diseases, such as atopic dermatitis, psoriasis, acne vulgaris, dandruff, and even skin cancer. Here, we focus on the associations between the microbiome, diet, metabolites, and immune responses in skin pathologies. This review describes an exhaustive list of common skin conditions with associated dysbiosis in the skin microbiome as well as the current body of evidence on gut microbiome dysbiosis, dietary links, and their interplay with skin conditions. An enhanced understanding of the local skin and gut microbiome including the underlying mechanisms is necessary to shed light on the microbial involvement in human skin diseases and to develop new therapeutic approaches.

Evaluation of different mucosal microbiota leads to gut microbiota-based prediction of type 1 diabetes in NOD mice

Type 1 diabetes (T1D) is a progressive autoimmune disease in which the insulin-producing beta cells are destroyed by auto-reactive T cells. Recent studies suggest that microbiota are closely associated with disease development. We studied gut, oral and vaginal microbiota longitudinally in non-obese diabetic (NOD) mice. We showed that the composition of microbiota is very different at the different mucosal sites and between young and adult mice. Gut microbiota are more diverse than oral or vaginal microbiota and the changes were more evident in the mice before and after onset of diabetes. Using alpha-diversity, Gram-positive/Gram-negative ratio as well as the relative abundance of Bacteroidetes and Erysipelotrichaceae in the gut microbiota, at 8 weeks of age, we formulated a predictive algorithm for T1D development in a cohort of 63 female NOD mice. Using this algorithm, we obtained 80% accuracy of prediction of diabetes onset, in two independent experiments, totaling 29 mice, with Area Under the Curve of 0.776 by ROC analysis. Interestingly, we did not find differences in peripheral blood mononuclear cells of the mice at 8 weeks of age, regardless of later diabetes development. Our results suggest that the algorithm could potentially be used in early prediction of future T1D development.

Electro-Acupuncture at Zusanli Acupoint (ST36) Suppresses Inflammation in Allergic Contact Dermatitis Via Triggering Local IL-10 Production and Inhibiting p38 MAPK Activation

Acupuncture has shown beneficial effect in the treatment of multiple dermatologic conditions including dermatitis, pruritus, urticaria, and hyperhidrosis; however, the detailed mechanisms are still kept unclear. This study aimed to investigate if electro-acupuncture (EA) treatment prevents 2,4-dinitrofluorobenzene (DNFB)-induced allergic contact dermatitis (ACD) in rats and explore its underlying mechanisms. ACD was induced by sensitizing and challenging with DNFB topically. Rats were treated daily following bilateral subcutaneous stimulation of EA at Zusanli acupoint (ST36) for 1 week. Ear swelling and serum IgE levels were measured. The ear biopsies were obtained for histology. Inflammatory cytokines on the dermatological ear and local acupoint tissue were assayed. Spleen lymphocytes and the homogenized supernatant of local acupuncture area were used to co-culture for flow cytology and immune analysis, respectively. EA treatment at ST36 notably inhibited ear swelling and inflammatory cell infiltration on DNFB-induced ACD. EA also decreased serum IgE concentrations and alleviated the production of inflammatory cytokines in dermatological ear. Additionally, EA treatment attenuated the percentage of CD4⁺IFN-γ⁺ and CD4⁺IL-4⁺ T cells associated with ACD. Interestingly, secretion of interleukin (IL)-10 in the local acupoint tissue following EA stimulation was increased and showed suppressive function when co-cultured with the spleen lymphocytes from DNFB group. Lastly, EA treatment demonstrably suppressed p38 MAPK activation in DNFB-treated rats. Our findings suggest that EA treatment at ST36 may ameliorate inflammation associated with DNFB-induced ACD via triggering local IL-10 production and inhibiting p38 MAPK activation, which provide an alternative and promising therapy for ACD.

TIM-4 is differentially expressed in the distinct subsets of dendritic cells in skin and skin-draining lymph nodes and controls skin Langerhans cell homeostasis

T cell immunoglobulin and mucin-4 (TIM-4), mainly expressed on dendritic cells (DC) and macrophages, plays an essential role in regulating immune responses. Langerhans cells (LC), which are the sole DC subpopulation residing at the epidermis, are potent mediators of immune surveillance and tolerance. However, the significance of TIM-4 on epidermal LCs, along with other cutaneous DCs, remains totally unexplored. For the first time, we discovered that epidermal LCs expressed TIM-4 and displayed an increased level of TIM-4 expression upon migration. We also found that dermal CD207⁺ DCs and lymph node (LN) resident CD207⁻CD4⁺ DCs highly expressed TIM-4, while dermal CD207⁻ DCs and LN CD207⁻CD4⁻ DCs had limited TIM-4 expressions. Using TIM-4-deficient mice, we further demonstrated that loss of TIM-4 significantly upregulated the frequencies of epidermal LCs and LN resident CD207⁻CD4⁺ DCs. In spite of this, the epidermal LCs of TIM-4-deficient mice displayed normal phagocytic and migratory abilities, comparable maturation status upon the stimulation as well as normal repopulation under the inflamed state. Moreover, lack of TIM-4 did not affect dinitrofluorobenzene-induced contact hypersensitivity response. In conclusion, our results indicated that TIM-4 was differentially expressed in the distinct subsets of DCs in skin and skin-draining LNs, and specifically regulated epidermal LC and LN CD207⁻CD4⁺ DC homeostasis.

Peptidoglycan in combination with muramyldipeptide synergistically induces an interleukin-10-dependent T helper 2-dominant immune response

In this study, peptidoglycan (PEG) from Staphylococcus aureus-stimulated, but not muramyldipeptide (MDP)-stimulated, Langerhans cells (LCs) induced a dose-dependent Th2-prone immune response. However, when LCs were stimulated with PEG in combination with MDP, the strength of Th2 immune responses was synergistically augmented by MDP. Furthermore, it was found that production of IL-10, but not of IL-12 p40, by PEG-stimulated LCs was also enhanced in the presence of MDP. These results suggest that MDP enhances Th2 cell development through up-regulation of IL-10 production from PEG-stimulated LCs, increase the importance of S. aureus colonization in patients with atopic dermatitis.

Peptidoglycan from Staphylococcus aureus has an anti-apoptotic effect in HaCaT keratinocytes mediated by the production of the cellular inhibitor of apoptosis protein-2

Colonization of epithelium by microorganisms leads to inflammatory responses. In some cases an anti-apoptotic response involving the cellular inhibitor of apoptosis protein-2 (cIAP-2) also occurs. Although strong expression of cIAP-2 has been observed in lesional skin from psoriatic patients and in HaCaT keratinocytes treated with peptidoglycan (PGN) from Staphylococcus aureus, anti-apoptotic responses induced in the skin by cIAP-2 have seldom been studied. In this study, the effect of PGN on TNF-α-induced apoptotic HaCaT keratinocytes was assessed. Morphological analysis, quantification of cells with DNA fragmentation and active caspase-3 detection was performed to assess apoptotic cell death. Greater LL-37 and cIAP-2 production was found in keratinocytes stimulated with PGN than in non-treated cells (P < 0.05). In comparison with cells treated with TNF-α only, a significant reduction in apoptotic cell death was observed when HaCaT were pretreated with PGN before inducing apoptosis with TNF-α (P < 0.05). In addition, an inhibitor of cIAP-2 activity (LCL161) stopped the PGN effect. These findings show that PGN from S. aureus has an anti-apoptotic effect in keratinocytes mediated by cIAP-2 production, suggesting that this anti-apoptotic activity could favor proliferation of keratinocytes in psoriasis.