Objective. In reactive arthritis (ReA) a bacteriaspecific T cell response to the triggering microbe is detected in synovial fluid (SF), and an impaired Th1 cytokine response has been described. The recent identification of immunodominant bacterial proteins/ peptides and new technologies make a more detailed analysis of the immune response possible. The aim of the present study was to use these new techniques to determine the antigen-specific T cell frequency and the cytokine secretion pattern on stimulation with bacteriaderived recombinant proteins in the peripheral blood (PB) and SF from patients with ReA.
Methods. In 3 patients with Chlamydia-induced ReA and 2 patients with Yersinia-induced ReA, the SF T cell response was investigated after stimulation with the Chlamydia-derived proteins major outer membrane protein (MOMP) and heat-shock protein 60 (Hsp60) and the Yersinia-derived proteins 19-kd protein and Hsp60. In 3 of these patients, the PB T cell response was investigated in parallel. T cells were stimulated in whole blood or whole SF with antigen plus anti-CD28 for 6 hours, brefeldin A was added after 2 hours, and cells were fixed and stained with antibodies against the surface markers CD4 and CD69 and against the cytokines interferon-␥ (IFN␥), tumor necrosis factor ␣, interleukin-10 (IL-10), and IL-4. Positive cells were quantified by flow cytometry.
Results. In the 3 patients with Chlamydia-induced
ReA, the antigen-specific T cell frequency (percentage of IFN␥ CD69 double-positive CD4؉ T cells) in response to MOMP (mean ؎ SD 1.2 ؎ 1.38%) and to Hsp60 (1.21 ؎ 1.45%) in SF was about the same. In the 2 patients with Yersinia-induced ReA, the mean ؎ SD frequency was 0.66 ؎ 0.36% in response to the Hsp60 and 0.3% ؎ 0.22 in response to the 19-kd protein. In the 3 patients whose PB was evaluated, the corresponding T cell response was >10 times lower. In 2 patients with Chlamydia-induced ReA, antigen-specific IL-10-positive CD4؉ T cells were detected in 0.10-0.23% of the CD4؉ T cell subpopulation.
Conclusion. The frequency of antigen-specific T cells to
Chlamydia-and Yersinia-derived antigens in the SF of ReA patients is between 1:200 and 1:50. Both the chlamydial Hsp60 and MOMP are dominant T cell antigens in Chlamydia-induced ReA. In patients with Chlamydia-induced ReA, we detected antigen-specific IL-10 secretion, which might mediate an inhibition of effective bacterial clearance.