A4: Epitope-dependent autoantibody-mediated skin inflammation in pemphigoid

Background. Bullous pemphigoid (BP) and mucous membrane pemphigoid (MMP) are associated with and caused by autoantibodies against BP180 (Lancet 381:320). The N-terminal, 16th non-collagenous domain (NC16A) of COL17 has been identified as immunodominant in BP. In MMP, however, C-terminal BP180 epitopes are primarily targeted. Anti-NC16A IgG induces a signal-transducing event that mediates cytokine and protease release from keratinocytes and recapitulates human BP when injected into mice. We recently generated mouse models duplicating human BP by injection anti-mouse NC15A (the mouse homologue of human NC16A), as well as an MMP model, where antibodies to all non-collagenous domains of COL17, except NC15A, induce experimental MMP in mice (Fig. A4-1). In addition, we and others noted the presence of BP180-specific antibodies in healthy individuals. Hence, we here will address whether the epitope-specificity of autoantibodies to the same autoantigen critically shapes the inflammatory reaction at a time point before skin/mucosal lesions occur.

Objectives. (i) Investigate differences in cellular events immediately after binding of IgG antibodies to different epitopes on BP180 derived from patients with active disease and in remission, as well as healthy individuals with BP180 antibodies. (ii) Specifically inhibit the identified cellular events induced by anti-BP180 antibodies targeting different epitopes. (iii) Analyze the effects of these epitope-specific antibodies in vivo.

Work program. We will incubate cultured human keratinocytes with IgG against different epitopes of human BP180 and from an already established cohort of healthy individuals with BP180 autoantibodies and patients with different disease phases. In cooperation with A9, cellular effects will be analyzed in a multi-OMICS approach. After validation, the identified cellular events will be inhibited by respective signal transduction inhibitors and gene silencing. Key experiments will be repeated using primary human keratinocytes. In parallel, the effect of IgG against different BP180 epitopes and different BP/MMP disease states will be compared after injection into mice with regard to the cellular infiltrate, gene expression, and proteomics in skin and oral mucosa before clinical lesions have appeared. Finally, inhibitors identified in the in vitro analyses will be applied in BP and anti-BP180 MMP mouse models.