Hypochlorous acid is antipruritic and anti-inflammatory in a mouse model of atopic dermatitis.

BACKGROUND: It has been reported that topical hypochlorous acid (HOCl) formulations lead to relief of itch in human patients with atopic dermatitis; however, the specific antipruritic mechanism of action remains unclear. OBJECTIVE: To confirm itch relief and reduction of lesions in a mouse model of atopic dermatitis and to elucidate possible HOCl's mode of action. METHODS: In this study, the effects of topical administration of HOCl hydrogel (0.05%) on atopic dermatitis-like lesions in NC/Nga mice model as well as in vitro effects of HOCl on dorsal root ganglia neurons and mouse bone marrow-derived dendritic cells (mBMDCs) were investigated. NC/Nga mice were sensitized with house dust mite allergen and treated topically with HOCl hydrogel both preventively and therapeutically against established lesions. Allergen challenge was continued during HOCl hydrogel application. RESULTS: Treatment with HOCl hydrogel prevented the development of lesions and scratching bouts during the whole observation period. When administered after full development of lesions, HOCl reduced lesions and scratching behaviour to a similar extent as a positive control 0.1% betamethasone dipropionate ointment. The reduced inflammatory response by HOCl treatment was demonstrated by reduced secretion of inflammatory cytokines in affected skin tissue from NC/Nga mice. In addition, HOCl significantly reduced IL-12 production in mBMDC. The diminished scratching behaviour was confirmed by impaired response to several pruritogens in dorsal root ganglia neurons excised from NC/Nga mice after termination of the studies. The response to the stimuli was also reduced by pre-incubation of sensory neurons from untreated BALB/c mice with 0.0001% HOCl. CONCLUSIONS AND CLINICAL RELEVANCE: These data indicate a direct reduction in sensory response by HOCl, leading to significantly reduced itch and inflammation in vivo.

The immunoglobulin superfamily member CD200R identifies cells involved in type 2 immune responses.

BACKGROUND: The pathology of allergic diseases involves type 2 immune cells, such as Th2, ILC2, and basophils exerting their effect by production of IL-4, IL-5, and IL-13. However, surface receptors that are specifically expressed on type 2 immune cells are less well documented. The aim of this investigation was to identify surface markers associated with type 2 inflammation. METHODS: Naïve human CD4+ T cells were short-term activated in the presence or absence of IL-4 and analyzed for expression of >300 cell-surface proteins. Ex vivo-isolated peripheral blood mononuclear cells (PBMCs) from peanut-allergic (PA) and nonallergic subjects were stimulated (14-16 h) with peanut extract to detect peanut-specific CD4+ CD154+ T cells. Biopsies were obtained for transcriptomic analysis from healthy controls and patients with extrinsic or intrinsic atopic dermatitis (AD) and psoriasis. RESULTS: Expression analysis of >300 surface proteins enabled identification of IL-4-upregulated surface proteins, such as CD90, CD108, CD109, and CD200R (CD200R1). Additional analysis of in vitro-differentiated Th0, Th1, and Th2 cultures identified CD200R as upregulated on Th2 cells. From ex vivo-isolated PBMCs, we found high expression of CD200R on Th2 and ILC2 cells and basophils. In PA subjects, the peanut-specific Th2 (CD154+ CRTh2+ ) cells expressed more CD200R than the non-allergen-specific Th2 (CD154- CRTh2+ ) cells. Moreover, costaining of CD161 and CD200R identified peanut-specific highly differentiated IL-4+ IL-5+ Th2 cells. Finally, transcriptomic analysis revealed upregulation of CD200R in lesional skin from subjects with an extrinsic AD phenotype compared to healthy skin. CONCLUSION: These results indicate that CD200R expression strongly correlates with Th2 pathology; though, the mechanism is as yet elusive.

Human Atopic Dermatitis Skin-derived T Cells can Induce a Reaction in Mouse Keratinocytes in vivo.

In atopic dermatitis (AD), the inflammatory response between skin-infiltrating T cells and keratinocytes is fundamental to the development of chronic lesional eczema. The aim of this study was to investigate whether skin-derived T cells from AD patients could induce an inflammatory response in mice through keratinocyte activation and consequently cause the development of eczematous lesions. Punch biopsies of the lesional skin from AD patients were used to establish skin-derived T cell cultures, which were transferred to NOD.Cg-Prkd(scid) Il2rg(tm1Sug) /JicTac (NOG) mice. We found that the subcutaneous injection of the human AD skin-derived T cells resulted in the migration of the human T cells from subcutis to the papillary dermis followed by the development of erythema and oedema in the mouse skin. Furthermore, the human T cells induced a transient proliferative response in the mouse keratinocytes shown as increased numbers of Ki-67(+) keratinocytes and increased epidermal thickness. Out of six established AD skin-derived T cell cultures, two were superior at inducing a skin reaction in the mice, and these cultures were found to contain >10% CCR10(+) T cells compared to <2% for the other cultures. In comparison, blood-derived in vitro-differentiated Th2 cells only induced a weak response in a few of the mice. Thus, we conclude that human AD skin-derived T cells can induce a reaction in the mouse skin through the induction of a proliferative response in the mouse keratinocytes.