Difference in the expression of IL-9 and IL-17 correlates with different histological pattern of vascular wall injury in giant cell arteritis

Objective. GCA is a large- and medium-vessel arteritis characterized by a range of histological patterns of vascular wall injury. The aim of this study was to immunologically characterize the various histological patterns of GCA. Methods. Thirty-five consecutive patients with biopsy-proven GCA and 15 normal controls were studied. IL-8, IL-9, IL-9R, IL-17, IL-4, TGF-β and thymic stromal lymphopoietin expression was evaluated by RT-PCR and immunohistochemistry on artery biopsy specimens. Confocal microscopy was used to characterize the phenotypes of IL-9-producing and IL-9R-expressing cells. Five additional patients who had received prednisone when the temporal artery biopsy was performed were also enrolled to evaluate the effect of glucocorticoids on IL-9 and IL-17 expression. Results. IL-17 overexpression was observed mainly in arteries with transmural inflammation and vasa vasorum vasculitis. IL-9 overexpression and Th9 polarization predominated in arteries with transmural inflammation and small-vessel vasculitis. The tissue expression of both IL-9 and IL-17 was correlated with the intensity of the systemic inflammatory response. IL-4, TGF-β and thymic stromal lymphopoietin, which are involved in the differentiation of Th9 cells, were overexpressed in arteries with transmural inflammation and small-vessel vasculitis. IL-9R was also overexpressed in GCA arteries with transmural inflammation and was accompanied by increased expression of IL-8. Conclusion. Herein we provide the first evidence that distinct populations of potentially autoreactive T cells, expressing different cytokines (Th17 vs Th9), characterize patients with particular histological subsets of GCA and may thus contribute to the heterogeneity of tissue lesions observed in these patients.