Background Atopic dermatitis (AD) is a T cell-mediated inflammatory skin disease, with TH2 cells initiating acute flares. This inflamed skin is immediately colonized with Staphylococcus aureus, which provides potent Toll-like receptor (TLR) 2 ligands. However, the effect of TLR2 ligands on the development of TH2-mediated AD inflammation remains unclear. Objective We investigated the progression of TH2 cell-mediated dermatitis after TLR2 activation. Methods Using models for acute AD with T H2 cells initiating cutaneous inflammation, we investigated the consequences of TLR2 activation. Dermatitis, as assessed by changes in ear skin thickness and histology, was analyzed in different BALB/c and C57BL/6 wild-type and knockout mouse strains, and immune profiling was carried out by using in vitro and ex vivo cytokine analyses. Results We show that TH2 cell-mediated dermatitis is self-limiting and depends on IL-4. Activation of TLR2 converted the limited TH2 dermatitis to chronic cutaneous inflammation. We demonstrate that the concerted activation of TLR2 and IL-4 receptor on dendritic cells is sufficient for this conversion. As an underlying mechanism, we found that the combinatorial sensing of the innate TLR2 ligands and the adaptive TH2 cytokine IL-4 suppressed anti-inflammatory IL-10 and consequently led to the exacerbation and persistence of dermatitis. Conclusion Our data demonstrate that innate TLR2 signals convert transient TH2 cell-mediated dermatitis into persistent inflammation, as seen in chronic human AD, through IL-4-mediated suppression of IL-10. For the first time, these data show how initial AD lesions convert to chronic inflammation and provide another rationale for targeting IL-4 in patients with AD, a therapeutic approach that is currently under development. © 2014 American Academy of Allergy, Asthma and Immunology.
Kaesler, S., Volz, T., Skabytska, Y., Köberle, M., Hein, U., Chen, K. M., … Biedermann, T. (2014). Toll-like receptor 2 ligands promote chronic atopic dermatitis through IL-4-mediated suppression of IL-10. Journal of Allergy and Clinical Immunology, 134(1). https://doi.org/10.1016/j.jaci.2014.02.017