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.

• [1] Mielants H, Veys EM, Cuvelier C, de Vos M. Ileocolonoscopic findings in seronegative spondylarthropathies. Br J Rheumatol. 1988; 27 Suppl 2:95-105.

• [2] 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.

• [3] 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