Expression of Interleukin-32 in the Inflamed Arteries of Patients With Giant Cell Arteritis

Giant cell (temporal) arteritis (GCA) is a vasculitis that mainly affects the large and medium arteries, especially the branches of the proximal aorta. Interleukin-32 (IL-32) is a recently described Th1 proinflammatory cytokine, and is mainly induced by interferon- (IFN ), IL-1 , and tumor necrosis factor (TNF ). This study was undertaken to investigate the expression and tissue distribution of IL-32 in artery biopsy specimens from patients with GCA. Methods. Quantitative gene expression analysis of IL-32, IL-1 , TNF , IFN , IL-6, and IL-27 was performed in artery biopsy specimens obtained from 18 patients with GCA and 15 controls. Immunohistochemistry analysis was performed to evaluate IL-32 tissue distribution and identify IL-32–producing cells. Circulating Th1 lymphocytes were evaluated by flow cytometry. Results. We demonstrated a strong and significant up-regulation of IL-32 at both the messenger RNA and protein levels in the artery biopsy samples from patients with GCA. IL-32 was abundantly expressed by vascular smooth muscle cells of inflamed arteries and neovessels within inflammatory infiltrates. IL-32 expression strongly correlated with the intensity of the systemic inflammatory response. IL-32 overexpression was accompanied by strong overexpression of Th1 cytokines, such as IFN and IL-27p28, in inflamed arteries from GCA patients. The Th1 lymphocyte population was also expanded among peripheral blood mononuclear cells from GCA patients and produced higher amounts of IL-32 compared to controls. Conclusion. Our findings indicate that overexpression of IL-32 together with a clear Th1 response immunologically characterizes the inflammatory response in GCA. In particular, IL-32 seems to be an important mediator of artery inflammation in GCA.