IntroductionIn this study, we analysed the number of IL-17+ cells in facet joints, in the peripheral blood (PB) and synovial fluid (SF) of spondyloarthritis (SpA) patients and compared these results with those of patients with other rheumatic diseases and controls.MethodsImmunohistochemical analysis of IL-17+ cells was performed in facet joints of 33 ankylosing spondylitis (AS) patients and compared with data from 20 osteoarthritis (OA) patients. The frequency of IL-17+CD4+ T cells in PB and SF of SpA patients (PB n = 30, SF n = 11), rheumatoid arthritis (RA) patients (PB n = 14, SF n = 7), OA patients (PB n = 10) and healthy controls (PB n = 12) was analysed after stimulation with Staphylococcus aureus Enterotoxin B and phorbol 12-myristate 13-acetate/ionomycin and quantified by flow cytometry.ResultsIn AS facet joints, the frequency of IL-17-secreting cells was significantly higher than in samples obtained from OA patients (P < 0.001), with a slight predominance of IL-17+ cells among the mononuclear cells (61.5% ± 14.9%) compared to cells with polysegmental nuclei. Immunofluorescence microscopy revealed that the majority of IL-17+ cells were myeloperoxidase-positive (35.84 ± 13.06/high-power field (HPF) and CD15+ neutrophils (24.25 ± 10.36/HPF), while CD3+ T cells (0.51 ± 0.49/HPF) and AA-1+ mast cells (2.28 ± 1.96/HPF) were less often IL-17-positive. The frequency of IL-17+CD4+ T cells in the PB and SF of SpA patients did not differ significantly compared to RA patients, OA patients or healthy controls.ConclusionsOur data suggest an important role for IL-17 in the inflammatory processes in AS. However, the innate immune pathway might be of greater relevance than the Th17-mediated adaptive immune response.

Our data show accumulation of Foxp3+ T cells within inflamed joints. These Foxp3+ T cells are mainly of stable T regulatory phenotype. The high frequency of Foxp3+ T cells in pSpA might contribute to the spontaneous resolution and remitting course of arthritis in pSpA as compared to the more persistent joint inflammation in RA.

E. coli is a target for polyclonal Th1 responses in healthy individuals. The impairment of these responses in CD and AS patients might be due to recruitment of enterobacteria-specific Th1 cells to the gut or might reflect inadequate priming of adaptive immune response.

The high frequency and enrichment of E coli-specific CD4 T cells in the inflamed joints of patients with AS but not those with RA suggests that commensal bacteria are relevant antigens in AS that might trigger the disease.

Background Ankylosing spondylitis (AS) is associated with clinical and subclinical mucosal inflammation suggesting that commensal bacteria contribute to the pathogenesis of the disease [1,2]. Objectives We determined the frequency of Th1 cells reacting towards conserved Escherichia coli (E. coli) proteins and pathogenicity factors in peripheral blood mononuclear cells (PBMNC) and synovial fluid mononuclear cells (SFMNC) of patients with AS and patients with rheumatoid arthritis (RA). As control, PBMNC of healthy individuals (HI) were included in the study. Methods All AS patients fulfilled the modified New York criteria. Peripheral blood or synovial fluid mononuclear cells were isolated by Ficoll density gradient centrifugation. For stimulation conserved proteins of E. coli were expressed and purified as described previously in detail [3]. PBMNC or SFMNC were stimulated with anti-CD28 in the presence or absence of the E. coli protein pool (10 proteins at 5 μg/ml) or pathogenicity factors espB and cesT. For polyclonal stimulation staphylococcus enterotoxin B (SEB) was used. CMV pp65 protein was used as a gut-unrelated protein antigen. Stimulation was performed for 6 hours with Brefeldin A added for the last 4 hours. Antigen-reactive Th1 cells were determined according to CD40L upregulation and IFNγ co-expression. Results In PBMNC and in particular in SFMNC of AS patients we detected higher frequencies of Th1 cells reacting to conserved E. coli proteins than in RA patients (PBMNC: p<0.05, SFMNC p<0.01). In contrast, the frequencies of CMV- and SEB-induced Th1 cells did not differ between AS and RA patients in SFMNC, and SEB-induced Th1 cell frequencies in PBMNCs were even higher in RA patients compared to AS patients (p<0.05). Conclusions The high frequency of E. coli-specific CD4+ T cells in the blood and in particular their enrichment in the inflamed joints of AS patients but not of RA patients suggests that commensal bacteria are relevant antigens in AS that might trigger the disease. References Mielants H, Veys EM, Cuvelier C, de Vos M. Ileocolonoscopic findings in seronegative spondylarthropathies. Br J Rheumatol. 1988; 27 Suppl 2:95-105. Mielants H, Veys EM, Cuvelier C, De Vos M, Goemaere S, De Clercq L, et al. The evolution of spondyloarthropathies in relation to gut histology. II. Histological aspects. J Rheumatol. 1995 Dec; 22(12):2273-2278. Ergin A, Bussow K, Sieper J, Thiel A, Duchmann R, Adam T. Homologous high-throughput expression and purification of highly conserved E coli proteins. Microb Cell Fact. 2007; 6:18. Disclosure of Interest None Declared