Outer membrane protein of salmonella is the major antigenic target in patients with salmonella induced reactive arthritis

Abstract

OBJECTIVE: We previously reported that Salmonella typhimurium was the triggering agent in one-third of our patients with sporadic enteric reactive arthritis (ReA) and undifferentiated spondyloarthropathy (uSpA). The antigens recognized by the synovial T cells in Salmonella induced ReA are not known. We investigated the immunodominant antigens in Salmonella ReA. METHODS: Synovial fluid mononuclear cells (SFMC) from 53 patients with ReA/uSpA were cultured with crude lysate of S. typhimurium. In 20 patients, the triggering agent was found to be Salmonella (stimulation index, SI, > 2.5). For cell fractionation of S. typhimurium, the sonicated crude lysate was separated by ultracentrifugation into a cytoplasmic supernatant (CYT) and membrane pellet (OMP). The CYT was further separated on SDS-PAGE and blotted onto nitrocellulose membrane for proliferation assays. SFMC from 20 patients with Salmonella ReA/uSpA were stimulated with OMP, CYT, and cytosolic fractions of S. typhimurium, and proliferation was measured by thymidine incorporation. Quantitation of antigen-specific cells in SF was by intracellular interferon-g staining in 7 patients and paired peripheral blood (PB) in 5 patients after stimulation with crude Salmonella lysate, CYT, and OMP. RESULTS: Out of 20 patients with Salmonella ReA/uSpA, the SFMC showed a significant proliferation to OMP in 19 patients and CYT in 17 patients. The median SI of OMP (8.2, range 2.8-52.5) was significantly higher (p < 0.0005) than for the CYT (4.9, 2.7-18.8). Fifty percent of the patients showed proliferative response to cytosolic fractions of < 60 kDa. The mean antigen-specific T cell frequency was also higher with OMP (0.68% +/- 0.59%) than CYT (0.53% +/- 0.62%) but this was not statistically significant. Compared to PB, the OMP-specific cells were 7.5 times more numerous in the SF (p < 0.05). CONCLUSION: The cellular immune response in Salmonella ReA/uSpA is directed predominantly against the OMP and low molecular weight proteins in the cytosolic fraction.