Increased expression of interleukin-22 in patients with giant cell arteritis.

Objectives: GCA is characterized by arterial remodelling driven by inflammation. IL-22 is an attractive cytokine which acts at the crosstalk between immune and stromal cells. We hypothesized that IL-22 might be induced in GCA and might be involved in disease pathogenesis.

Methods: Patients subjected to temporal artery biopsies (TABs) naïve from therapy were enrolled: 27 biopsy-proven GCA, 8 biopsy-negative GCA, 21 biopsy-negative non-GCA patients. Expression of IL-22 was determined in TABs by immunohystochemistry, in plasma by ELISA, in peripheral blood mononuclear cells by real-time PCR and flow cytometry. Effects of IL-22 on viability and gene expression of primary cultures obtained from TABs were also evaluated.

Results: Inflamed TABs from GCA patients showed a higher expression of IL-22 and IL-22 specific receptor subunit (IL-22R1) than non-inflamed TABs. IL-22 was expressed in infiltrating immune cells and spindle shaped cells, IL-22R1 was expressed in endothelial cells. Patients with biopsy-proven GCA showed increased levels of IL-22 in plasma than patients with biopsy-negative GCA, without GCA and healthy subjects. Peripheral blood mononuclear cells from GCA patients expressed higher IL-22 transcript than healthy subjects. After stimulation in vitro with phorbol 12-myristate 13-acetate and ionomycin, the frequencies of Th22 and IL-22+ CD4+ lymphocytes were similar between patients with and without GCA. Treatment with IL-22 of primary cultures obtained from TABs increased cell viability under stress conditions and expression of B-cell activating factor.

Conclusion: IL-22 is increased in patients with GCA and affects viability and gene expression of arterial cells, supporting a potential role in disease pathogenesis.