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

Area of Science:

• Immunology
• Dermatology
• Auto-inflammatory diseases

Background:

• Hidradenitis suppurativa (HS) is a chronic inflammatory skin condition with complex immune system involvement.
• The role of complement activation in HS pathogenesis remains unclear, with conflicting evidence on local versus systemic involvement.

Purpose of the Study:

• To investigate local complement deposition in HS skin lesions.
• To evaluate the expression of complement components (C1q, C3c, C4d, C5b-9, properdin) and C5a receptor 1 (C5aR1) in HS tissues.

Main Methods:

• Direct immunofluorescence was used to detect complement deposition (C1q, C3c, C4d, C5b-9, properdin) in skin biopsies from 19 HS patients and 6 controls.
• Immunohistochemistry was employed to visualize C5aR1 expression on immune cells within the lesions.

Main Results:

• No significant local deposition of C1q, C3c, C4d, C5b-9, or properdin was observed in HS lesions compared to controls.
• C5aR1 expression was found on immune cells, primarily neutrophils, with no significant difference in relative abundance within the infiltrate compared to controls.

Conclusions:

• This study did not confirm local complement deposition in HS skin using standard techniques.
• The increased presence of C5aR1-expressing immune cells suggests a role for complement in HS pathogenesis, supporting targeted therapies.