Bullous pemphigoid-associated S. aureus increases protease activity from keratinocytes and promotes unique BP180 cleavage

Summary: Abstract Body: Staphylococcus (S.) aureus has been found to routinely colonize the skin of individuals with bullous pemphigoid (BP). A defining characteristic of BP is subepidermal blistering, which is caused by loss of function of the hemidesmosomal protein BP180. We hypothesized that S. aureus virulence factors facilitate loss of BP180 function from keratinocytes (KC) through diminished expression and/or enhanced cleavage. While host proteases have been shown to cleave BP180, the role of microbiome-associated proteases has not been considered. Adult primary KC from 22-70 years of age were exposed to complex mixtures of virulence factors from S. aureus strains isolated from BP skin, or routinely used in research. We observed that virulence factors from multiple BP-associated S. aureus isolates induced a novel cleavage pattern of BP180 rarely seen in conditions with control strains. A modest association between the ratio of cleaved to full length BP180 and donor age was observed in untreated conditions (n = 14 donors, Spearman R value = 0.4741, p=0.0885). However, when this comparison was conducted on samples exposed to S. aureus virulence factors (BP isolate), this relationship became more robust (n = 9 donors, Spearman R value = 0.6527, p=0.0635). KC exposed to BP-associated S. aureus virulence factors significantly increased expression of the protease MMP9 (2.11 ± 1.43-fold, p≤0.05) and demonstrated elevated protease activity in supernatants (3.26 ± 2.27-fold, p≤0.05). Virulence factors from BP-associated S. aureus strains also uniquely promoted expression of the alarmin IL33 from KC, which was significantly increased (10.84 ± 10.75-fold, p≤0.01) when combined with type 2 cytokines IL-4 + IL-13. These findings suggest an important role for the cutaneous microbiome in BP pathogenesis. We anticipate these observations will lead to novel interventions that improve BP disease, which are desperately needed for this population. For example, targeting specific S. aureus virulence factors directly may provide an efficacious treatment for BP patients. Annaliese H. Hersom¹, Alice P. Pentland¹, Matthew G. Brewer¹ 1. Dermatology, University of Rochester Medical Center, Rochester, NY, United States. Innate Immunity, Microbiology, and Microbiome