Decreased Serum Level of Interleukin-22 Correlates with Hepcidin in Patients with Hidradenitis Suppurativa

Current understanding of the underlying pathophysiology of hidradenitis suppurativa (HS) links the disease with proinflammatory activation and autoimmune processes. This study investigated serum levels of interleukin (IL)-22, a cytokine critically involved in epithelial homeostasis, in the context of the broad clinical spectrum of patients with HS. The study also assessed the relationship between serum IL-22 and pro-inflammatory activation (as evidenced by serum level of IL-6) and serum hepcidin (central regulator of systemic iron homeostasis). Serum concentrations of IL-22 were assessed in 74 patients with HS and 15 healthy subjects. Compared with healthy controls, patients with HS demonstrated decreased levels of serum IL-22 (median; interquartile range (IQR): 12.4 pg/ml (9.8; 23.5) vs 34.8 pg/ml (24.8; 39.8), p < 0.001 vs controls). Disease severity (assessed both with Hurley staging and Hidradenitis Suppurativa Severity Index) did not differentiate IL-22 levels (p > 0.1 in both comparisons). Serum levels of IL-22 and IL-6 did not correlate with each other (R=–0.17, p = ns). In a subgroup of 24 patients with HS with pro-inflammatory activation, the mean level of IL-22 was similar to that of the remaining patients (median (IQR): 9.8 pg/ml (8.5; 15.0) vs 12.0 pg/ml (9.4; 16.3), p = ns). Patients with HS demonstrated a decreased level of hepcidin (mean: 31.3 ± 25.9 pg/ml), which correlated with the levels of IL-22 (R=0.36, p < 0.05). Patients with HS demonstrated significantly decreased levels of serum IL-22, which was neither correlated with pro-inflammatory status nor associated with disease severity, but correlated modestly with serum hepcidin.