Spondyloarthropathies Contributes to HLA-B 27-associated Unfolded Protein Response in γ Interferon-1

Objective. 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. Methods. 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-g (IFN-g) 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) Results. 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-g were found to have activated the HLA-B27 promoter in the U937 cell line (p < 0.05). Following stimulation with IFN-g, 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). Conclusion. 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-g significantly activated HLA-B27 promoter in the U937 cell line, and IFN-g, the strongest activating factor, may induce the UPR in HLA-B27-expressing cells. (First Release Jan 15 2012; J Rheumatol 2012;39:574–82; doi:10.3899/ jrheum.101257) Key Indexing Terms: HLA-B27 SPONDYLOARTHROPATHY TUMOR NECROSIS FACTOR-α INTERFERON-g UNFOLDED PROTEIN RESPONSE From the Department of Clinical Immunology, State Key Discipline of Cell Biology, Xijing Hospital, Fourth Military Medical University, Xi’an, Shaanxi Province, China. Y. Feng, PhD; J. Ding, PhD; C.M. Fan, BA; P. Zhu, MD, Professor, Department of Clinical Immunology, State Key Discipline of Cell Biology, Xijing Hospital, Fourth Military Medical University. Dr. Feng and Dr. Ding contributed equally to this work. Address correspondence to Dr. P. Zhu, Department of Clinical Immunology, State Key Discipline of Cell Biology, Xijing Hospital, Fourth Military Medical University, 15 Changlexi Road, Xi’an, Shaanxi Province, China. E-mail: zhuping@fmmu.edu.cn Accepted for publication October 17, 2011. Spondyloarthropathies (SpA) are a cluster of interrelated and overlapping chronic inflammatory rheumatic diseases that primarily include ankylosing spondylitis (AS), reactive arthritis (ReA), psoriatic arthritis (PsA), and inflammatory bowel disease arthritis. SpA commonly cause inflammation of the spine, eye, bowel, genital tract, or skin. SpA present striking familial aggregations and are typically associated with HLA genes, particularly HLA-B271,2. But it remains unclear how HLA-B27 contributes to arthritis. Different hypotheses have been formulated to explain this association: among them, the presentation of exogenous or self-peptides to HLA-B27+CD8+ T cells, the antigen presentation by HLA-B27 free heavy-chain homodimers, and HLA-B27 misfolding and the endoplasmic reticulum unfolded protein response (ER UPR)3. In addition, other mechanisms such as interaction of cell-surface dimers with killer cell Ig-like receptors (KIR) have been shown by Bowness, et al4. These hypotheses are all based on the activities of HLA-B27 protein. It is believed that in addition to certain other genes and/or environmental factors, the degree of expression of the HLA-B27 gene is also responsible for the susceptibility to SpA. Taurog, et al have shown that in HLA-B27*05 transgenic rats, the degree of susceptibility of various lines to the development of an SpA-like spectrum of lesions correlates with the level of HLA-B27 transgene expression at the mRNA and protein levels5. Cauli, et al reported that the expression of HLA-B27 molecule on the surface of peripheral blood mononuclear cells (PBMC) was higher in patients with AS than in HLA-B27-positive healthy volunteers6. However, very little research has been conducted to investigate HLA-B27 gene regulation.