S100A9 and histiocytic sarcoma: In a summary of HS research during the last 15 years in the European Hidradenitis Suppurativa Foundation official journal, authors found downregulation of alarmins/antimicrobial peptides of S100A and S100A9 and increased expression of antimicrobial cathelicidins LL-37 in HS lesional skin, suggesting innate barrier dysfunction and development of altered host-microbiome crosstalk [111].