Objective: In reactive arthritis (ReA), a bacteria-specific T cell response to the triggering microbe is detected in synovial fluid. So far, direct characterization of bacteria-specific T cells and identification of the immunodominant fine specificities remain difficult due to the lack of appropriate techniques. The aim of the present study was to directly determine the fine specificity of CD4+ T cells specific to ReA-associated bacteria-derived protein.
Methods: In 2 patients with Yersinia-induced ReA, live Yersinia Hsp60-specific CD4+ T cells were directly isolated from synovial fluid after stimulation with Yersinia-derived protein Hsp60 using a cytometric cytokine secretion assay. Generated short-term T cell lines were then tested in vitro for their peptide epitope specificity. Also, direct cross-reactivity of one line with Chlamydia- and human-derived Hsp60 was assessed.
Results: Generated short-term CD4+ T cell lines were highly antigen-specific and revealed single immunodominant peptide epitopes that were confirmed by direct testing with single peptides in both peripheral blood and synovial fluid cells. Yersinia Hsp60-specific T cells of one patient cross-reacted directly with human Hsp60.
Conclusion: Our results demonstrate the feasibility of direct assessment of live, potentially pathogenic, antigen-specific interferon-gamma+ CD4+ T cells taken from inflammatory lesions of patients with rheumatic diseases such as ReA. This might have implications not only regarding pathogenesis, but also in the design of new immunotherapies.