Skin microbiota-associated inflammation precedes autoantibody induced tissue damage in experimental epidermolysis bullosa acquisita
Introduction
Epidermolysis bullosa acquisita (EBA) is a chronic, prototypic organ-specific autoimmune bullous dermatosis (AIBD) characterized by antibodies targeting type VII collagen (COL7), a major component of the dermal–epidermal junction (DEJ) [1], [2], [3], [4]. Evidence from in vitro models, animal experiments and patient material identified COL7 as the target antigen in EBA and the pathogenic relevance of anti-COL7 autoantibodies has been established both in vitro and in vivo [5], [6], [7], [8], [9]. Both innate and adaptive immune responses are involved in disease development. For example, while binding of the Fab fragment alone to its target structure cannot induce a clinically overt disease in experimental models of the disease [8], [9], several studies have shown that Fc-mediated activation of the complement system and Fc-gamma-receptor (FcgR)-dependent degranulation of neutrophils are required to produce disease symptoms [6], [10]. In addition, the adaptive immune system plays an essential role. Immunization with a recombinant fragment of murine COL7 results in autoantibody production in almost all tested strains [11]. Clinical disease with subepidermal blister formation only occurs when associated with a Th1-like immune response and is linked to the H2s haplotype [12], [13].
However, although inbred SJL/J mice carry the H2s haplotype and 100% of them produce autoantibodies after immunization with COL7, only 80% develop skin blisters. Twenty percent remain healthy despite the same genetic background and identical environmental conditions [11], [12]. The lack of disease development in a considerable proportion of immunized animals cannot be explained by the current understanding of experimental EBA pathogenesis. This suggests the presence of a so far unknown factor which may modulate innate and/or adaptive immune responses in such a way that 20% of the animals are protected from development of overt clinical disease. In this context extrinsic triggers that locally influence the development of an immune response might play a role. Indeed, it has been shown that skin microbiota are able to regulate the production of cytokines such as IL-1 by cells derived from healthy skin [14] and to modulate the clinical course of skin disorders such as psoriasis [15] and atopic dermatitis [16].
Based on these observations, we analyzed the development of clinical symptoms in EBA-susceptible SJL/J mice, studied the contribution of the innate and adaptive immune response, and investigated the role of the skin microbiota. We found that in genetically identical mice, housed under highly standardized conditions, skin blistering depends on the influence of the local skin milieu on the innate immune system. An increased richness and diversity of the skin microbiota before immunization appear to prevent blister formation. This observation underlines the importance of host–environment interaction in regulating the transition from autoimmunity to autoimmune disease.
Section snippets
Despite presence of autoantibodies, 20% of SJL/J mice do not develop skin blisters
After immunization with COL7, 100% of SJL/J mice showed circulating autoantibodies in the blood against COL7. The majority of these mice developed overt skin blistering disease. However, 20% of immunized mice remained clinically healthy lacking cutaneous inflammation (Fig. 1A). The frequency of diseased and healthy mice was randomly distributed across different cages and experiments and mice were held under identical environmental conditions. Both healthy and mice with skin blisters showed
Discussion
Despite autoantibody production in all immunized SJL/J mice, clinically overt skin blistering is observed in only 80% of mice. Interestingly, the remaining 20% of the mice do not develop skin blisters. Here, we provide evidence that blister formation in genetically identical mice housed under highly standardized conditions is controlled by the local milieu of the skin and its effects on the innate immune response.
Analysis of the skin of immunized mice revealed that both healthy mice and mice
Mice
Female SJL/J mice were obtained from Charles River Laboratories (Sulzfeld, Germany). At the beginning of the experiments mice were 8–10 weeks old. Housing facilities were according to FELASA recommendations with a dark:light cycle of 12:12 h, an ambient temperature of 23 ± 1 °C and a humidity of 65 ± 5%. Housing of the mice was performed under conventional husbandry practices in open-box cages on metal racks. SPF-conditions were ensured throughout the experiments without any detection of before
Acknowledgments
This work was supported by grants from the Excellence Cluster “Inflammation at Interfaces” (DFG, EXC306/1 and 2), Research Training Group (RTG) “Modulation of Autoimmunity” (DFG, GRK1727), and the University of Lübeck Focus Program “Autoimmunity”. We thank Lidija Gutjahr, Marie-Luise Leppin, and Karola von Lingelsheim for excellent technical assistance.
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