Identification of Immunogenic HLA-B*27:05 Binding Peptides of Salmonella Outer Membrane Protein in Patients with Reactive Arthritis and Undifferentiated Spondyloarthropathy

Abstract

Salmonella outer membrane proteins (OMP) are major immunogenic targets to synovial fluid lymphocytes of patients with reactive arthritis (ReA)/undifferentiated spondyloarthropathy (uSpA). Because these patients have genetic predisposition to HLA-B*27 and its subtype HLA-B*27:05, we sought to identify immunogenic HLA-B*27:05-binding salmonella OMP peptides in patients with ReA/uSpA. A total of 125 HLA-B*27:05-binding salmonella OMP peptides identified using ProPred-I software were synthesized and grouped in 23 pools. The peptide pools, along with crude enteric bacterial lysates and salmonella OMP, were cultured with synovial fluid (SF) or peripheral blood mononuclear cells (PBMC) from 23 patients with ReA/uSpA, 10 with rheumatoid arthritis (RA), and 10 healthy individuals in 96-well culture plates. Proliferation was measured by tritiated thymidine uptake and interferon-γ (IFN-γ) levels in culture supernatant. Individual peptides from pools having significant responses were retested with cryopreserved cells. Immunogenic peptides thus identified were further tested in 5 additional new patients with ReA/uSpA by flow cytometry. A Basic Local Alignment Search Tool program was used to search for similar peptides from a protein bank of arthritogenic bacteria and human protein. Nineteen of 23 SFMC from ReA/uSpA showed a significant proliferative response to salmonella OMP, with minimal response of PBMC (1/10) from ReA/uSpA, SFMC from RA (1/10), or PBMC from controls (1/10). Nine salmonella OMP peptides, QRAEMLPTL, SRSGLNIAL, LRFLYAKSL, RLEGTWVKL, ARCIAPYAL, KLFLTTAAL, YRNSDFFGL, QRPAVRVKL, and YRVGPGDVL, were identified. Response to QRAEMLPTL was seen in 6/7 HLA-B*27:05-positive patients. All immunogenic peptides had sequence similarity with peptides from arthritogenic bacterial proteins, while 5 had similarity with peptides from human proteins. Nine novel immunogenic OMP peptides binding to HLA-B*27:05 were identified that showed sequence similarity with other arthritogenic bacteria.