Serum levels of interleukin-32 and interleukin-6 in granulomatosis with polyangiitis and microscopic polyangiitis: association with clinical and biochemical findings.

BACKGROUND: Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is an autoimmune disorder of unknown etiology with dysregulated cytokines levels.

OBJECTIVES: The main aim of this study was to assess the clinical correlation between antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, granulomatosis with polyangiitis (GPA) serum levels of the microscopic polyangiitis (MPA), serum levels of the proinflammatory cytokines, interleukin (IL)-32 and interleukin-6.

METHODS: Study included 71 patients, 47 with GPA and 24 with MPA. Serum IL-32 and IL-6 concentrations were analyzed in all patients, and compared with levels observed in 10 controls. IL-32 and IL-6 were evaluated using DuoSet and Quantikine HS ELISA, respectively. IL-32 and IL-6 concentrations were correlated with disease-related clinical and laboratory findings.

RESULTS: IL-32 and IL-6 levels were significantly higher in GPA and MPA than in controls, especially IL-32 levels in GPA were elevated. IL-32 concentrations correlated positively with anti-proteinase 3 - ANCA (PR3-ANCA) levels in GPA (P < 0.0001), and with anti-myeloperoxidase ANCA (MPO-ANCA) in MPA (P = 0.049). IL-32 levels correlated positively with disease activity in GPA and MPA (P < 0.0001). GPA patients with pulmonary, cutaneous, and musculoskeletal involvement presented the highest IL-6 serum levels. Cutaneous manifestations correlated positively with IL-6 levels in MPA patients (P = 0.05). ANCA-positive patients with GPA expressed significantly high IL-6 levels (P = 0.036). No significant difference in IL-32 values was observed between ANCA-positive and ANCA-negative patients.

CONCLUSIONS: Patients with GPA and MPA present higher serum IL-32 and IL-6 levels than controls. IL-32 levels correlate positively with disease activity.