Abstract: Outer Membrane Protein of Salmonella Is the Major Antigenic Target in Patients with Salmonella Induced Reactive Arthritis

Outer Membrane Protein of Salmonella Is the Major Antigenic Target in Patients with Salmonella Induced Reactive Arthritis

SHWETA SAXENA, AMITA AGGARWAL, and RAMNATH MISRA

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. (J Rheumatol 2005;32:86-92)

Key Indexing Terms:

IMMUNE RESPONSE
ENTERIC BACTERIA
SERONEGATIVE SPONDYLOARTHROPATHY

From the Department of Immunology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India.

Supported by an Intramural Research Grant to Dr. R. Misra.

S. Saxena, MSc (Biotechnology), PhD Student; A. Aggarwal, DM (Clinical Immunology), Associate Professor of Clinical Immunology; R. Misra, MD (Medicine), Professor of Clinical Immunology.

Address reprint requests to Prof. R. Misra, Department of Immunology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, 226 014 India. E-mail: rnmisra@sgpgi.ac.in

Submitted June 13, 2003; revision accepted August 10, 2004.