Interferon-γ contributes to HLA-B27-associated unfolded protein response in spondyloarthropathies

HLA-B27 positivity strongly influences the susceptibility to and phenotype of spondyloarthropathies (SpA). This study was designed to screen factors that activate the promoter of HLA-B27 in U937 cells, and to assess whether these promoter-activating factors induce the unfolded protein response (UPR) in HLA-B27-expressing cells.

Cytometric Bead Array, flow cytometry, and real-time polymerase chain reaction were used to detect the expression of cytokines and UPR-associated proteins in peripheral blood and synovial fluid of patients with SpA. The HLA-B27 promotor transfectant was incubated separately with cytokines and Toll-like receptor ligands. After interferon-γ (IFN-γ) stimulation, expressions of GRP78, CHOP, and XBP-1 were tested in HLA-B27-expressing U937 cells and peripheral blood mononuclear cell (PBMC) of patients with ankylosing spondylitis (AS). (Clinical trial registration no. ChiCTR-OCC-11001565)

Expressions of GRP78, CHOP, and XBP-1 in monocytes/macrophages of SpA peripheral blood and synovial fluid were higher than those in healthy controls and patients with osteoarthritis (OA) (p < 0.05). Tumor necrosis factor-α (TNF-α) and IFN-α, IFN-ß, and IFN-γ were found to have activated the HLA-B27 promoter in the U937 cell line (p < 0.05). Following stimulation with IFN-γ, the expressions of GRP78, CHOP and XBP-1 in HLA-B27-transfected U937 cells and PBMC of HLA-B27-positive AS patients were more intense than those in A2-U937 cells, HLA-B27-negative AS patients, or healthy controls (p < 0.05).

Expressions of GRP78, CHOP, and XBP-1 were higher in monocytes/macrophages of patients with SpA than those in both OA patients and healthy controls, suggesting that UPR may participate in the pathogenesis of SpA. TNF-α and IFN-α, IFN-ß, and IFN-γ significantly activated HLA-B27 promoter in the U937 cell line, and IFN-γ, the strongest activating factor, may induce the UPR in HLA-B27-expressing cells.