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Surfactant-induced cumulative irritant contact dermatitis (ICD) is a common and clinically important skin disorder. CCL2 is known to mediate inflammation after tissue damage in various organs. Thus, we investigated whether and how CCL2 contributes to the development of murine cumulative ICD induced by a common surfactant, SDS. Wild-type mice treated topically with SDS for 6 consecutive days developed skin inflammation that recapitulated the features of human cumulative ICD, including barrier disruption, epidermal thickening, and neutrophil accumulation. CCL2 was upregulated in SDS-treated skin, and local CCL2 blockade attenuated SDS-induced ICD. SDS-induced ICD and neutrophil accumulation were also attenuated in mice deficient in CCR2, the receptor for CCL2. Neutrophil depletion alleviated SDS-induced ICD, suggesting that impaired neutrophil accumulation was responsible for the amelioration of ICD in CCR2-deficient mice. In RNA-sequencing analyses of SDS-treated skin, the expression levels of Il1b in Ccr2-deficient mice were highly downregulated compared with those in wild-type mice. Furthermore, the intradermal administration of IL-1β in the SDS-treated skin of CCR2-deficient mice restored the local accumulation of neutrophils and the development of ICD. Collectively, our results suggest that CCL2‒CCR2 signaling in the skin critically promotes the development of SDS-induced ICD by inducing IL-1β expression for neutrophil accumulation., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

It is challenging to investigate neutrophil extracellular traps (NETs) and bacterial colonization in vivo. Bitschar et al. (2020) oppose an existing paradigm regarding neutrophils in host defense and propose that neutrophils increase Staphylococcus aureus skin colonization through NETs, not by trapping microbes but via indirect mechanisms. These results are open to interpretation and should stimulate productive discussions., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

A large number of gamma delta T cells (γδ T cells) are located within epithelial tissues including the skin. In mice, epidermal and dermal γδ T cells consist of distinct subsets and have specific roles in cutaneous immune responses. A recent study demonstrated that γδ T cells and cutaneous dendritic cells migrate from the skin to the draining lymph nodes (LNs). However, it remains unclear whether they regulate the antigen-specific immune response within the LNs. Herein, we investigated their properties and role in the LNs using the Mycobacterium bovis bacille Calmette-Guérin (BCG) infection model. In vivo cell labeling analysis revealed that most of the migratory subset comprised dermal Vγ4(+) cells. This population transmigrated from the skin to the LNs in a Gi-coupled chemokine receptor-independent manner. By depleting Vγ4(+) cells, the intranodal expansion of CD8(+) T cell against BCG was significantly attenuated. In addition, in vitro analysis revealed that Vγ4(+) cells produced TNF-α and enhanced IL-12 production by dendritic cells. Taken together, these findings suggest that dermal Vγ4(+) cells are a unique subset that possesses a migratory potency to the skin-draining LNs and enhances the dendritic cell function therein.

Contact hypersensitivity (CHS) has been widely used to study cutaneous immune responses, as a prototype of delayed-type hypersensitivity. Although natural killer T (NKT) cells have been assumed to have an important role in CHS, their role is controversial. Here, we report the role of NKT cells in the sensitization phase of CHS, by promoting the survival and maturation of dendritic cells (DCs) in the draining lymph nodes (LNs). The CHS response was attenuated with Cd1d1(-/-) and Traj18(-/-) BALB/c mice in which NKT cells were absent. In the draining LNs, the number of effector T cells and cytokine production were significantly reduced with NKT cell-deficient mice. NKT cells activated and colocalized with DCs in the draining LNs after sensitization. The number of migrated and mature DCs was reduced in NKT cell-deficient mice 72 hours after FITC application. In in vitro experiments, activated NKT cells enhanced bone marrow-derived DC (BMDC) survivability via tumor necrosis factor (TNF) production from BMDCs. In addition, TNF production from BMDCs was partially suppressed by the neutralizing anti-CD54 or CD154 antibodies. Our data demonstrate that DC-NKT interaction has a pivotal role in the sensitization phase of CHS.

Atopic dermatitis (AD) is generally regarded as a type 2 helper T (Th2)-mediated inflammatory skin disease. Although the number of IL-17A-producing cells is increased in the peripheral blood and in acute skin lesion of AD patients, the role of IL-17A in the pathogenesis of AD remains unclear. To clarify this issue, we used murine AD models in an IL-17A-deficient condition. In a repeated hapten application-induced AD model, skin inflammation, IL-4 production in the draining lymph nodes (LNs), and hapten-specific IgG1 and IgE induction were suppressed in IL-17A-deficient mice. Vγ4(+) γδ T cells in the skin-draining LNs and Vγ5(-) dermal γδ T cells in the skin were the major sources of IL-17A. Consistently, in flaky-tail (Flg(ft/ft) ma/ma) mice, spontaneous development of AD-like dermatitis and IgE induction were attenuated by IL-17A deficiency. Moreover, Th2 differentiation from naive T cells was promoted in vitro by the addition of IL-17A. Taken together, our results suggest that IL-17A mediates Th2-type immune responses and that IL-17A signal may be a therapeutic target of AD.

In organ culture experiments, the induction of pemphigus acantholysis is known to be blocked by the addition of serine proteinase inhibitors. Recently, nontoxic synthesized low molecular weight proteinase inhibitors have been clinically available for the treatment of disseminated intravascular coagulation and pancreatitis. To determine if these drugs are useful aids to treat patients with pemphigus, we examined the effect of omega-guanidino ester analogues, i.e., 1) gabexate mesilate, 2) camostat mesilate, and 3) nafamostat mesilate, on experimental pemphigus acantholysis in both organ culture and neonatal BALB/c mice. Furthermore, the effect of plasma natural proteinase inhibitors (alpha-1-proteinase inhibitor) isolated from human plasma was similarly examined. Results revealed that synthesized low molecular weight inhibitors (drugs) were able to inhibit the induction of acantholysis in organ culture system, but had little or no effect on lesion formation in the neonatal mouse system. By contrast, alpha-1-proteinase inhibitor could completely inhibit acantholysis formation in mice. These findings implied a possible new therapeutic approach using proteinase inhibitors for patients with pemphigus.