Analysis of the mechanism for the development of allergic skin inflammation and the application for its treatment:keratinocytes in atopic dermatitis - their pathogenic involvement

Cutaneous dysbiosis may amplify barrier dysfunction in patients with atopic dermatitis

Atopic dermatitis (AD) is associated with cutaneous dysbiosis, barrier defects, and immune dysregulation, but the interplay between these factors needs further study. Early-onset barrier dysfunction may facilitate an innate immune response to commensal organisms and, consequently, the development of allergic sensitization. We aimed to compare the cutaneous microbiome in patients with active dermatitis with and without a history of childhood flexural dermatitis (atopic dermatitis). Next-gen Ion-Torrent deep-sequencing identified AD-associated changes in the skin bacterial microbiome ("bacteriome") and fungal microbiome ("mycobiome") of affected skin in swabs from areas of skin affected by dermatitis. Data were analyzed for diversity, abundance, and inter-kingdom correlations. Microbial interactions were assessed in biofilms using metabolic activity (XTT) assay and scanning electron microscopy (SEM), while host-pathogen interactions were determined in cultured primary keratinocytes exposed to biofilms. Increased richness and abundance of Staphylococcus, Lactococcus, and Alternaria were found in atopics. Staphylococcus and Alternaria formed robust mixed-species biofilms (based on XTT and SEM) that were resistant to antifungals/antimicrobials. Furthermore, their biofilm supernatant was capable of influencing keratinocytes biology (pro-inflammatory cytokines and structural proteins), suggesting an additive effect on AD-associated host response. In conclusion, microbial inter-kingdom and host-microbiome interactions may play a critical role in the modulation of atopic dermatitis to a greater extent than in non-atopic adults with allergic contact dermatitis.

Keratinocytes: An Enigmatic Factor in Atopic Dermatitis

Atopic dermatitis (AD), characterized by rashes, itching, and pruritus, is a chronic inflammatory condition of the skin with a marked infiltration of inflammatory cells into the lesion. It usually commences in early childhood and coexists with other atopic diseases such as allergic rhinitis, bronchial asthma, allergic conjunctivitis, etc. With a prevalence rate of 1–20% in adults and children worldwide, AD is gradually becoming a major health concern. Immunological aspects have been frequently focused on in the pathogenesis of AD, including the role of the epidermal barrier and the consequent abnormal cytokine expressions. Disrupted epidermal barriers, as well as allergic triggers (food allergy), contact allergens, irritants, microbes, aggravating factors, and ultraviolet light directly initiate the inflammatory response by inducing epidermal keratinocytes, resulting in the abnormal release of various pro-inflammatory mediators, inflammatory cytokines, and chemokines from keratinocytes. In addition, abnormal proteinases, gene mutations, or single nucleotide polymorphisms (SNP) affecting the function of the epidermal barrier can also contribute towards disease pathophysiology. Apart from this, imbalances in cholinergic or adrenergic responses in the epidermis or the role played by immune cells in the epidermis such as Langerhans cells or antigen-presenting cells can also aggravate pathophysiology. The dearth of specific biomarkers for proper diagnosis and the lack of a permanent cure for AD necessitate investigation in this area. In this context, the widespread role played by keratinocytes in the pathogenesis of AD will be reviewed in this article to facilitate the opening up of new avenues of treatment for AD.

House Dust Mites Induce Production of Endothelin-1 and Matrix Metalloproteinase-9 in Keratinocytes via Proteinase-Activated Receptor-2 Activation

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by skin barrier dysfunction and abnormal immune response. House dust mites (HDM) are a major source of allergens, some of which have cysteine and serine protease activities. Keratinocytes stimulated by HDM-derived proteases have been suggested to contribute to the pathogenesis of AD by producing various cytokines. However, whether keratinocytes contribute to the induction of pruritus in AD, especially by producing pruritus-related mediators upon stimulation with HDM-derived proteases, has not been fully elucidated.

METHODS

We examined whether the production of endothelin-1 (ET-1), matrix metalloproteinase (MMP)-2, and MMP-9 in keratinocytes can be induced by stimulation with Dermatophagoides farinae extracts, and if so, whether pretreatment with a protease inhibitor or proteinase-activated receptor-2 (PAR-2) antagonist affects the production of these mediators in keratinocytes.

RESULTS

Although MMP-2 levels were undetectable in the culture supernatants, the production of ET-1 and MMP-9 was increased upon stimulation with HDM extracts in a concentration- and time-dependent manner and suppressed by pretreatment of HDM extracts with serine protease inhibitor, but not with cysteine protease inhibitor. Mite-derived serine proteases also induced ET-1 and MMP-9 production in a concentration- and time-dependent manner. Moreover, pretreatment with a PAR-2 antagonist inhibited the production of ET-1 and MMP-9 in keratinocytes.

CONCLUSION

These results suggest that the activation of PAR-2 on keratinocytes by HDM-derived serine proteases induces the production of ET-1 and MMP-9, and may contribute to the induction of pruritus in AD.

Effects of Ambient Fine Particles PM2.5 on Human HaCaT Cells

The current study was conducted to observe the effects of fine particulate matter (PM_2.5) on human keratinocyte cell line (HaCaT) cells. The potential mechanism linking PM_2.5 and skin was explored. HaCaT cells were cultured and then accessed in plate with PM_2.5. Cell viability was tested by Cell Counting Kit-8. The mRNA and protein expression of Filaggrin, Loricrin, Involucrin, and Repetin were analyzed. The levels of Granulocyte-macrophage Colony Stimulating Factor, Thymic Stromal Lymphopoietin, Tumor Necrosis Factor-α, Interleukin-1α, and Interleukin-8 were detected in the supernatant of the HaCaT cell with enzyme-linked immunosorbent assay kits. Cell viability decreased with the increase in PM_2.5. Compared with the control group, the protein expression of Filaggrin, Repetin, Involucrin, and Loricrin showed different expression patterns in PM_2.5 treatment groups. The level of Tumor Necrosis Factor-α, Thymic Stromal Lymphopoietin, Interleukin-1α, and Interleukin-8 significantly increased in the cells treated with PM_2.5. Ambient PM_2.5 may increase the risk of eczema and other skin diseases. The relative mechanism may be associated with the impairment of the skin barrier and the elevation of inflammatory responses.

Dissecting the causes of atopic dermatitis in children: less foods, more mites

Atopic dermatitis (AD) is a common, chronic or chronically relapsing, multifactorial skin disease that mainly occurs in children but affects also adults. AD usually begins early in life and often concerns people with a personal or family history of asthma and allergic rhinitis. AD is characterized by eczematous changes in the epidermis and originates from a late, T-cell mediated reaction associated to the formation and production of memory T-cell of TH2 type, occurrence of homing receptor at skin level and cutaneous lymphocyte-associated (CLA) antigens. Extrinsic or allergic AD, but not intrinsic AD, shows high total serum IgE levels and the presence of specific IgE for environmental and food allergens. A pivotal role in the pathogenesis of AD is played by filaggrin, a protein contained in the granular layer of the epidermis regulating the aggregation of keratin filaments. Mutation in the filaggrin gene causes decreased barrier function of the corny layers of the epidermis. This favours the enter through the skin of environmental allergens, especially the house dust mite, that further facilitates such entering by the proteolytic activity of its major allergen Der p 1. In fact, recent advances suggest that the dust mite, more than foods, is the major cause of allergic AD. As far as the causal diagnosis of AD is concerned, there is notable evidence supporting the capacity of the atopy patch test (APT) to reproduce the pathophysiologic events of AD. This makes APT a valuable diagnostic tool for AD.

Assessment of chemokine profiles in human skin biopsies by an immunoaffinity capillary electrophoresis chip

Atopic dermatitis is a skin condition resulting in a skin rash from exposure to environmental factors. Skin biopsies taken from patients suffering from atopic dermatitis were micro-dissected and analyzed using a microchip-based immunoaffinity CE system for the presence of CXCL1, CXCL5 and CXCL8 and CCL1, CCL3 and CCL5 chemokines. Disposable immunoaffinity disks with immobilized antibodies were used to capture the CXC and CC chemokines from the homogenized skin samples. The captured analytes were then labeled with AlexaFluor 633, eluted from the disk and separated by CE. The labeled chemokines were identified and quantified by laser induced fluorescence. The total analysis time was less than 40min, including the biopsy microdissection, pre-analysis preparation of the sample and the ICE-CHIP analysis, which took less than 10min with inter- and intra-assay CV's below 6.4%. Microchip-based immunoaffinity CE could distinguish between normal skin biopsies and those with inflammation. Patients with neutrophil cellular infiltrates by histopathology showed increased concentrations of CXCL1, CXCL5 and CXCL8 while increases of CCL1, CCL3 and CCL5 corresponded to the patient group demonstrating monocytic and T-lymphocyte infiltration by histopathology. This system demonstrates the ability to identify and quantify immunochemical analytes in frozen sections taken from clinical histopathology samples.

Filaggrin knockdown and Toll-like receptor 3 (TLR3) stimulation enhanced the production of thymic stromal lymphopoietin (TSLP) from epidermal layers

Keratinocytes constitute the first-line barrier against exogenous antigens and contain Toll-like receptors (TLRs), which function as pattern-recognition molecules to activate antimicrobial innate immune responses. In an effort to ascertain whether or not filaggrin (filament-aggregating protein) expression affected the TLR-mediated responses of keratinocytes, we transfected filaggrin siRNA into HaCaT human keratinocyte cells and determined that thymic stromal lymphopoietin (TSLP) and IL-6 secretion were increased by poly(I:C) stimulus. Additionally, TSLP expression is increased in filaggrin knockdown as well as TLR3 stimulation in reconstituted human epidermal layers. Therefore, the findings of this study show that reduced filaggrin levels may influence innate immune responses via TLR stimuli and may contribute to the pathogenesis of inflammatory skin disease via TSLP expression.

Atopic dermatitis and keratoconjunctivitis

Atopic dermatitis, a chronic disease seen by allergist-immunologists, has both dermatologic and ocular manifestations. The ocular component is often disproportionately higher than the dermatologic disease. Even if skin abnormalities seem well controlled, these patients require ophthalmic evaluation. Atopic keratoconjunctivitis in atopic dermatitis patients is characterized by acute exacerbations and requires maintenance therapy for long-term control. Future studies will continue to emphasize the use of steroid-sparing, immunomodulating agents that have the potential to provide long-lasting anti-inflammatory control with a more favorable side-effect profile.