Innate Immune Regulation of Dermatitis

The Interaction between the Host Genome, Epigenome, and the Gut-Skin Axis Microbiome in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease that occurs in genetically predisposed individuals. It involves complex interactions among the host immune system, environmental factors (such as skin barrier dysfunction), and microbial dysbiosis. Genome-wide association studies (GWAS) have identified AD risk alleles; however, the associated environmental factors remain largely unknown. Recent evidence suggests that altered microbiota composition (dysbiosis) in the skin and gut may contribute to the pathogenesis of AD. Examples of environmental factors that contribute to skin barrier dysfunction and microbial dysbiosis in AD include allergens, irritants, pollution, and microbial exposure. Studies have reported alterations in the gut microbiome structure in patients with AD compared to control subjects, characterized by increased abundance of Clostridium difficile and decreased abundance of short-chain fatty acid (SCFA)-producing bacteria such as Bifidobacterium. SCFAs play a critical role in maintaining host health, and reduced SCFA production may lead to intestinal inflammation in AD patients. The specific mechanisms through which dysbiotic bacteria and their metabolites interact with the host genome and epigenome to cause autoimmunity in AD are still unknown. By understanding the combination of environmental factors, such as gut microbiota, the genetic and epigenetic determinants that are associated with the development of autoantibodies may help unravel the pathophysiology of the disease. This review aims to elucidate the interactions between the immune system, susceptibility genes, epigenetic factors, and the gut microbiome in the development of AD.

Neural Regulation of Innate Immunity in Inflammatory Skin Diseases

As the largest barrier organ of the body, the skin is highly innervated by peripheral sensory neurons. The major function of these sensory neurons is to transmit sensations of temperature, pain, and itch to elicit protective responses. Inflammatory skin diseases are triggered by the aberrant activation of immune responses. Recently, increasing evidence has shown that the skin peripheral nervous system also acts as a regulator of immune responses, particularly innate immunity, in various skin inflammatory processes. Meanwhile, immune cells in the skin can express receptors that respond to neuropeptides/neurotransmitters, leading to crosstalk between the immune system and nervous system. Herein, we highlight recent advances of such bidirectional neuroimmune interactions in certain inflammatory skin conditions.

Efficacy and safety of topical JAK inhibitors in the treatment of atopic dermatitis in paediatrics and adults: A systematic review

Atopic dermatitis (AD) is the most common skin inflammatory disease. Dysregulation of innate and adaptive immune systems plays a major role in the pathophysiology of AD. JAKi (Janus Kinase Inhibitors) reduce the production of pro-inflammatory cytokines and represent a promising novel treatment for AD. To assess and summarize the overall efficacy and safety of topial JAKi in the treatment of AD in adults and pediatrics, a broad search was performed on Ovid Medline, Ovid Embase, Cochrane Library, Web of Sciences, Scopus, CINAHL and Google Scholar until 14 June 2022. After screening, 19 studies remained for the final review. The current systematic review was conducted according to PRISMA, and the protocol was registered in PROSPERO (ID #CRD42022303321). Topical delgocitinib, tofacitinib, ruxolitinib, cerdulatinib and ifidancitinib are effective in treating AD and significantly improve EASI, IGA, pruritus-NRS score and some other indexes in adults. Moreover, topical delgocitinib was observed to have a great efficacy in the treatment of AD in paediatrics. All topical JAKi showed minimal risk of mild-to-moderate adverse effects. Available topical JAKi are effective and safe modalities in treating AD. Nevertheless, further studies with longer duration and head-to-head comparative trials are necessary to find the best option with the least adverse effects.

Water Extract of Senecio scandens Buch.-Ham Ameliorates Pruritus by Inhibiting MrgprB2 Receptor

Background

Senecio scandens Buch.-Ham (S. scandens) belongs to the Compositae family. As a Traditional Chinese medicine, S. scandens has been used in China to treat conjunctivitis, mastitis and vaginitis, it also has the function of antibacterial and relieving itching.

Methods

Water extract of S. scandens (WSS) was prepared and its quality was controlled by HPLC. The antipruritic effects of WSS were evaluated by itch behavioral experiments. The oxazolone and compound 48/80 were induced to mice scratch behavior, scratch was recorded 30 min after sensitization. The relationship between the antipruritic mechanism and MrgprB2 on mast cell was studied by using mast cell-deficient Kit (W-sh) “Sash” mice and MrgprB2^−/− mice. The mast cells were observed by toluidine blue staining. In vitro, the effects of WSS on MrgprB2 were studied by calcium imaging; The whole-cell patch clamp method recorded the MrgprB2 mediate voltage-dependent currents in mast cells.

Results

The content of rutin (0.012%) and hyperin (0.014%) in the WSS were determined. WSS could ameliorate the pruritus induced by Oxazolone (inhibition was 41.19%, p = 0.004) and compound 48/80 (inhibition was 50.29%, p = 0.001). Meanwhile, WSS could reduce the number of mast cells in mice skin tissue with allergic contact dermatitis (ACD) (p = 0.002) or compound 48/80 (p = 0.013). In addition, WSS could inhibit the calcium influx (1 mg/mL: p = 0.001, 3 mg/mL: p < 0.0001) and the voltage-dependent currents induced by activation of MrgprB2 on mast cell. WSS also attenuated the calcium influx induced by compound 48/80 in HEK293 cells overexpressing MrgprB2/X2.

Conclusion

These results showed that WSS could ameliorate pruritus by inhibiting MrgprB2 receptor on mast cells.

Soluble mediators in the function of the epidermal-immune-neuro unit in the skin

Skin is the largest, environmentally exposed (barrier) organ, capable of integrating various signals into effective defensive responses. The functional significance of interactions among the epidermis and the immune and nervous systems in regulating and maintaining skin barrier function is only now becoming recognized in relation to skin pathophysiology. This review focuses on newly described pathways that involve soluble mediator-mediated crosstalk between these compartments. Dysregulation of these connections can lead to chronic inflammatory diseases and/or pathologic conditions associated with chronic pain or itch.

Potential roles of gut microbial tryptophan metabolites in the complex pathogenesis of acne vulgaris

Acne vulgaris is a chronic inflammatory skin disease in which the influence of gut microbiota has been implicated but without clarification of mechanisms. Gut microbiota may exert such an influence via metabolites, particularly those of tryptophan. End metabolites of tryptophan activate receptors, including aryl hydrocarbon, G protein-coupled, and pregnane X receptors to stabilize the immune microenvironment and intestinal mucosal homeostasis. Any impact on the pathogenesis of acne vulgaris remains unclear. The current review collates recent advances concerning potential roles of tryptophan metabolism in mediating skin inflammation, follicular sebaceous gland function and intestinal permeability, all of which influence the pathogenesis of acne vulgaris. The aim was to improve understanding of the pathogenesis of acne vulgaris and to expose therapeutic opportunities.

Identification of Effective Diagnostic Biomarkers and Immune Cell Infiltration in Atopic Dermatitis by Comprehensive Bioinformatics Analysis

Background: Atopic dermatitis (AD) is a dermatological disorder characterized by symptoms such as chronically inflamed skin and frequently intolerable itching. The mechanism underlying AD development is still unclear. Our study aims to identify the diagnostic and therapeutic biomarkers for AD and provide insight into immune mechanisms at the molecular level through bioinformatics analysis.

Methods: The GSE6012, GSE32924, and GSE36842 gene expression profiles were obtained for analysis from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were segregated using the “Batch correction” and “RobustRankAggreg” methods. Weighted gene co-expression network analysis (WGCNA) was performed to screen for module genes with AD traits. Then, common DEGs (co-DEGs) were screened out via combined differential expression analysis and WGCNA. Functional enrichment analysis was performed for these co-DEGs using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG), followed by protein-protein interaction network analysis. Candidate hub genes were identified using the “cytoHubba” plugin in Cytoscape, and their value for AD diagnosis was validated using receiver operating characteristic curve analysis in the external database GSE120721. Immunohistochemical staining was performed for further validation. The CIBERSORT algorithm was used to evaluate skin samples obtained from healthy controls (HCs) and lesions of AD patients, to determine the extent of immune cell infiltration. The association between the identified hub genes and significant differential immune cells was analyzed using Pearson correlation analysis.

Results: A total of 259 DEGs were acquired from the intersection of DEGs obtained by the two independent procedures, and 331 AD-trait module genes were separated out from the blue module via WGCNA analysis. Then, 169 co-DEGs arising from the intersection of the 259 DEGs and the 331 AD-trait module genes were obtained. We found that co-DEGs were significantly enhanced in the type I interferon and IL-17 signal transduction pathways. Thirteen potential hub genes were identified using Cytoscape. Five hub genes (CCR7, CXCL10, IRF7, MMP1, and RRM2) were identified after screening via external dataset validation and immunohistochemical analysis. We also identified four significant differential immune cells, i.e., activated dendritic cells, plasma cells, resting mast cells, and CD4+ naïve T cells, between AD patients and HCs. Moreover, the relationship between the identified hub genes and significant differential immune cells was analyzed. The results showed that the CCR7 expression level was positively correlated with the number of CD4+ naïve T cells (R = 0.42, p = 0.011).

Conclusion: CCR7, CXCL10, IRF7, MMP1, and RRM2 could be potential diagnostic and therapeutic biomarkers for AD. CCR7 expression level was positively correlated with the number of CD4+ naïve T cells in AD. These findings need to be corroborated in future studies.

The Role of Cord Blood in the Regulation of the Cellular and Humoral Link of Immunity in Experimental Atopic Dermatitis

Background. Atopic dermatitis (AD) as one of the most common diseases of autoimmune genesis in the structure of dermatological practice, is characterized by itching, dryness, thickening of the skin, characteristic rashes. The drugs of choice in the treatment of AD are steroidal anti-inflammatory drugs. However, the development of unwanted side effects is a serious problem attributed to using hormone therapy. The search for effective methods of treating AD is an urgent task of medicine and in particular dermatology. At the same time, there is an obvious need for the participation in the solution of this problem also of specialists-immunologists working in the field of application of cell therapy drugs, acting on various pathogenetic links of the disease. The development of new or optimization of existing methods of treating AD is the urgent task facing them. Objective. Evaluation of the immunocorrective effect of lyophilized (lHCBL) and cryopreserved human cord blood leucoconcetrate (cHCBL) on a AD model. Methods. The experiments were carried out on 6-month-old Wistar rats. Upon induction of AD, the inflammation focus was formed on the rat's back (9–10 cm2) by daily rubbing in a 5% alcohol-acetone solution of dinitrochlorobenzene (DNCB) for 21 days. cHCBL and lHCBL were injected intraperitoneally, 0.5 ml at a dose of 5´106 cells in one day after the final DNCB treatment. The adhesive and phagocytic activity of the cells of the peritoneal cavity, the level of circulating immune complexes, the population and subpopulation of lymphocytes (CD3+, CD4+, CD8+, CD16+, CD4+CD25+), the immunoregulatory index of lymphocytes, the concentration of immunoglobulins in the blood serum were determined. Results. For AD induced by DNCB, systemic changes in the immune status are characteristic, which is expressed by changes in the parameters of cellular and humoral immunity. The most fundamental changes in cell subpopulations in spleen of rats with AD were revealed: a decrease in the number of total T-lymphocytes and their two main subpopulations (CD4+ and CD8+ cells). Against this background, changes were noted in the monocytic-phagocytic and humoral systems of immunity. The paper shows the effectiveness of the use of cHCBL and lHCBL in the correction of pathological manifestations of experimental AD. On the background of treatment, the features of the immunocorrective effect of each of the drugs were noted. Thus, when assessing intergroup values, a more pronounced increase in T-reg was revealed in rats of the 5th group – 3.9 [3.8; 4.0] versus 3.2 [3.0; 3.3] in the 4th group (P < 0.01); IgA level – 1.6 [1.5; 1.7] versus 1.3 [1.2; 1.4] (P < 0.01). Conclusions. Thus, lHCBL exhibits immunocorrective activity in the treatment of experimental AD, surpassing in some parameters the activity of сHCBL, which is promising for its use in clinical practice.