Apocrine gland damage and the release of specific keratins in early stage indicate the crucial involvement of apocrine glands in hidradenitis suppurativa.

The apocrine glands (AGs) are not considered to be primarily involved in hidradenitis suppurativa (HS). This study investigated the potential role of AGs in HS pathogenesis using immunohistochemistry and single-cell sequencing of nonlesional skin (NLS) and early lesional skin (LS) from patients with HS (n = 12) and healthy controls (HC, n = 8). AG cell destruction was more frequent and AG size was significantly reduced in the NLS and LS. Barrier-related genes (e.g., claudin 1 and E-cadherin) were downregulated in the AGs of the NLS and LS. Damaged AGs in the LS primarily recruit and activate neutrophils via the CXCL-CXCR and SAA1-FPR2 pathways. Elevated levels of specific keratins (KRT18 and KRT19) released from damaged AGs were observed on the skin surface of patients and were associated with disease severity. KRT19 was also detected in the dermis of the NLS and LS and was surrounded by neutrophils and macrophages. Moreover, serum KRT19 levels in patients (n = 20) were significantly negatively correlated with the age at HS onset. Collectively, our findings provide previously unreported evidence that the AGs are damaged and release specific keratins in early HS lesions, indicating a crucial role of the AGs in HS pathogenesis.