Impact of innate immunity on pemphigus vulgaris disease manifestation

Pemphigus vulgaris is a chronic autoimmune blistering disease characterized by antibody production against Desmogleins 3 (Dsg3) and 1 (Dsg1) causing acantholysis. Increased levels of innate cytokines detected in the blister fluid suggest a role of innate immune system activity. To elucidate the discrepancy between binding of pathogenic antibodies and a lack of blister formation, we focused on the role of innate cofactors supporting acantholysis. Here, we used a dispase-based keratinocyte-dissociation assay with a human immortalized keratinocyte cell line (HaCaT) and human primary keratinocytes. Besides fragmentation, the induction of innate cytokines was detected by RT-PCR and ELISA. To transfer these in vitro conditions to a more physiological setting, we performed studies ex vivo with human skin explants. We were able to identify factors inducing the innate immune system (UVA, bacterial toxins, Poly I:C) which enhance acantholysis induced by the anti-Dsg3 antibody AK23. Ex vivo, we observed a synergistic effect of AK23 (subpathogenic level) and UVA (non-toxic intensity). The augmented acantholysis in vitro and ex vivo as well as cytokine release seem to be caspase-dependent as these effects were reversible by (pan-)caspase inhibitors. Interestingly, recombinant IL-1 itself did not increase fragmentation in vitro, adding to the hypothesis that not the cytokine but rather an up-stream signaling event could be pathogenetically relevant. Our findings lead us to the conclusion that innate immune activation might favor autoantibody induced blister formation. The execution of acantholysis depends on caspase activation and most probably inflammasome activation. The molecular components of these signaling pathways could be possible therapeutic targets in disease management.