Low molecular weight proteins of outer membrane of Salmonella typhimurium are immunogenic in Salmonella induced reactive arthritis revealed by proteomics

Summary In patients with reactive arthritis (ReA)/undifferentiated spondyloarthropathy (uSpA), synovial fluid mononuclear cells (SFMC) show proliferation to bacterial antigens that trigger ReA, i.e. Chlamydia , Yersinia , Campylobactor , Shigella and Salmonella species. We have shown previously that SFMC proliferate significantly to outer membrane proteins of S typhimurium in Salmonella induced ReA. In the present study we characterized the immunoreactive fractions of outer membrane protein (Omp) of S typhimurium in Salmonella induced ReA. Omp of Salmonella was isolated and fractionated by continuous elution sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) using Prep‐Cell into eight Omp fractions based on molecular weight. Twenty‐three patients with ReA were screened for the bacterial trigger using the SFMC proliferative response to crude lysates of Y enterocolitica, S flexneri, C jejuni and S typhimurium using thymidine uptake assay. SFMC from patients with salmonella induced ReA were tested against eight fractions. Seven of 23 patients with ReA had S typhimurium‐ induced ReA. Of these seven patients, five patients SFMC had a significant stimulation index (SI) against < 22, 22–26, 25–35 and 28–40 kDa fractions of Omp. These fractions were analysed by SDS‐PAGE and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectrometry, which revealed 10 proteins. These proteins were 37 kDa OmpA, 33 kDa TsX, 28 kDa putative Omp, 28 kDa Vac J, 39 kDa OmpD, 18 kDa OmpX, 23 kDa OmpW, 43 kDa OmpS1 and 19 kDa peptidoglycan‐associated lipoprotein. In conclusion, for the first time we have identified some low molecular weight proteins in the Omps of Salmonella which are T cells immunoreactive in patients with salmonella induced ReA/uSpA.