Pre‐existing inflammation reduces the response to contact allergens in Tmem79‐deficient mice
Authors: Mia Hamilton Jee, Anders Boutrup Funch, Julie Friis Weber, Kelvin Yeung, Veronika Mraz, Anne‐Sofie Østergaard Gadsbøll, Tinghuan Song, Anders Woetmann, Niels Ødum, Jeanne Duus Johansen, Carsten Geisler, Charlotte Menné Bonefeld
Journal: Allergy (2024)

It is still a major question whether patients with atopic dermatitis (AD) have an altered response to contact allergens compared to controls without AD.1, 2 In an effort to address this question, we compared the response to the contact allergen 1-fluoro-2,4-dinitrobenzene (DNFB) in wild-type (WT), Flgft/ft and Tmem79ma/ma mice in a well-established model for allergic contact dermatitis (ACD).3 Flgft/ft and Tmem79ma/ma mice have defects in the skin barrier, but in contrast to Flgft/ft mice, Tmem79ma/ma mice spontaneously develop skin inflammation dominated by IL17-producing T cells4, 5 (Figures S1 and S2). Thus, in the present study WT mice represent healthy skin, Flgft/ft mice represent skin with an impaired skin barrier without skin inflammation, and Tmem79ma/ma mice represent skin with impaired skin barrier and pre-existing skin inflammation. Sensitization with DNFB generated similar numbers of pathogenic epidermis-resident CD8+ memory T (TRM) cells in Flgft/ft and Tmem79ma/ma mice as in WT mice as determined by flow cytometry at Day 21 after sensitization (Figure 1A,B), whereas it did not affect the number of epidermal CD4+ TRM cells that was constitutively increased in Tmem79ma/ma mice (Figures 1C and S1J). The mice were challenged with DNFB at Day 21 and in accordance with previous studies,3 the inflammatory response peaked 24 h after the challenge. However, the peak response in Tmem79ma/ma mice was significantly reduced compared to WT and Flgft/ft mice (Figure 1D). The inflammatory response is dependent on CD8+ TRM cells and recruitment of neutrophils.3 We found reduced neutrophil recruitment to the epidermis of Tmem79ma/ma mice compared to WT mice (Figure 1E), although the numbers of CD8+ TRM cells after DNFB challenge were similar in the groups (Figure 1F). In parallel with the impaired inflammatory response and recruitment of neutrophils, the expression of il1b, cxcl5 and ifng was reduced in the skin of Tmem79ma/ma mice compared to WT mice (Figure 1G). Furthermore, exposure to DNFB slightly down-regulated il17a expression in Tmem79ma/ma (Figure 1G). The observation of similar numbers of CD8+ TRM cells but a 5–10 fold reduction in IFNγ suggested that active suppression of the CD8+ TRM cells took place in the skin of the Tmem79ma/ma mice resulting in impaired chemokine production and neutrophil recruitment. Accordingly, Tmem79ma/ma mice had higher numbers of CD4+ T cells, including FoxP3+CD25+CD4+ Treg cells, in the epidermis compared to WT mice (Figure 1H,I). The number of FoxP3+CD25+CD4+ Treg cells generally correlated with the expression levels of il10 (Figure 1G,I). To distinguish the effect of circulating from epidermal-resident Treg cells, we took advantages of the observation that infusion of T-cell depletion antibodies effectively eliminates circulating T cells while sparing tissue-resident T cells6 (Figure 2A). Depletion of circulating CD4+ T cells resulted in an enhanced challenge response in the mouse strains. However, the response in the Tmem79ma/ma mice was still reduced compared to the responses in WT and Flgft/ft mice (Figure 2B) despite higher numbers of CD8+ TRM cells in Tmem79ma/ma mice (Figure 2C). The numbers of CD4+ TRM cells and FoxP3+CD25+CD4+ Treg cells were significantly higher in the epidermis of Tmem79ma/ma mice than in WT mice (Figure 2D,E), supporting that pre-existing Treg cells in the skin suppressed the immune response to DNFB in Tmem79ma/ma mice. In conclusion, our study demonstrates that pre-existing skin inflammation, as seen in AD patients, can result in anti-inflammatory mechanisms that suppress immune responses to new allergens/antigens. Further studies should determine whether this is general for all allergens/antigens. We believe that our observations are relevant for future research in the role of pro- and anti-inflammatory mechanisms in contact allergy and in the development of dermal vaccines. Conceptualization of this study was led by MHJ and CMB and supported by JDJ, CG, NØ and AW. Formal analysis was led by MHJ and supported by CMB, CG, ABF, JFW and KY. Funding acquisition was done by CMB, CG and JDJ. Investigation was led by MHJ and supported by ABF, JFW, KY, TS, VM and AG. Methodology was led by MHJ and CMB and supported by CG. Project administration was done by MHJ. Resources were obtained by CMB and CG. Supervision was done by CMB and supported by JDJ. Validation was led by MHJ and supported by ABF, JFW, KY and TS. Visualization was done by MHJ. Writing of the original draft was done by MHJ, CMB and CG. Review and editing were done by all authors. We would like to thank Rebecca Kitt Davidson Lohmann for her excellent technical support. This study was supported by The Danish Environmental Protection Agency, The LEO Foundation, The A.P. Møller Foundation for the Advancement of Medical Science and The Aase and Ejnar Danielsen Foundation. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request. Data S1. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.