Complement activation in Hidradenitis suppurativa: Covert low-grade inflammation or innocent bystander?

Hidradenitis suppurativa (HS) is a chronic auto-inflammatory skin disease with a complex and multifactorial pathogenesis involving both the innate and adaptive immune system. Despite limited evidence for local complement activation, conflicting results have been published on the role of systemic complement activation in HS. It was hypothesized that complement was consumed in highly inflamed HS skin, trapping complement from the circulation. Therefore, the aim of this study was to evaluate this local complement deposition in HS skin lesions using routine and commonly used complement antibodies.Direct immunofluorescence for C1q, C3c, C4d, C5b-9, and properdin was performed on frozen tissue sections of 19 HS patients and 6 controls. C5a receptor 1 (C5aR1) was visualized using immunohistochemistry. Overall, we found no significant local complement deposition in HS patients versus controls regarding C1q, C3c, C4d, C5b-9, or properdin on either vessels or immune cells. C5aR1 expression was exclusively found on immune cells, predominantly neutrophilic granulocytes, but not significantly different relatively to the total infiltrate in HS lesions compared with controls. In conclusion, despite not being able to confirm local complement depositions of C1q, C3c, C4d, or properdin using highly sensitive and widely accepted techniques, the increased presence of C5aR1 positive immune cells in HS suggests the importance of complement in the pathogenesis of HS and supports emerging therapies targeting this pathway.

Adalimumab and infliximab survival in patients with hidradenitis suppurativa: a daily practice cohort study.

BACKGROUND: Biologics are often required for the treatment of hidradenitis suppurativa (HS). However, data on the drug survival of biologics in daily practice are currently lacking. OBJECTIVES: To assess the drug survival of antitumour necrosis factor biologics in a daily practice cohort of patients with HS and to identify predictors for drug survival. METHODS: A retrospective multicentre study was performed in two academic dermatology centres in the Netherlands. Adult patients with HS using biologics between 2008 and 2020 were included. Drug survival was analysed with Kaplan-Meier survival curves and predictors of survival with univariate Cox regression analysis. RESULTS: The overall drug survival of adalimumab (n = 104) at 12 and 24 months was 56·3% and 30·5%, respectively, which was predominantly determined by infectiveness. Older age (P = 0·02) and longer disease duration (P < 0·01) were associated with longer survival time. For infliximab (n = 44), overall drug survival was 58·3% and 48·6% at 12 and 24 months, respectively, and was predominantly determined by infectiveness and side-effects. Surgery during treatment was associated with a longer survival time (P = 0·01). CONCLUSIONS: Survival rates were comparable for adalimumab and infliximab at 12 months, and were mainly determined by ineffectiveness. Age, disease duration (adalimumab) and surgery (infliximab) are predictors for longer survival.