The role played by the microbiota in pathogenesis of Hidradenitis suppurativa (HS), a chronic inflammatory skin condition characterized by recurrent abscesses and discharging sinus tracts, is unknown. HS skin harbor a polymicrobial flora that is distinctively enriched in uncommon anaerobes like Porphyromonas asaccharolytica (Pa). To determine if the host immune system perceives this cutaneous dysbiosis, we analyzed serum immunoglobulin (Ig) reactivity against a panel of bacteria representing lesional and healthy skin microbiomes. We identified in severe cases a distinctive IgG/IgA reactivity against HS-associated anaerobes, including Pa. Severe cases also displayed abnormally high levels of secretory IgA in serum, some reacting against Pa, suggesting a bacterial invasion across the skin barrier. In situ detection of bacterial RNAs in lesional skin revealed an active colonization of keratinocytes and recruited plasmocytes by Pa. Together, these data demonstrate that Pa is a skin invader and a catalyst of immune dysregulation in severe HS.

Paris post-doc seminar series.