peptidoglycan is a persistent antigen in patients with Lyme arthritis.

Lyme disease is a multisystem disorder caused by the spirochete A common late-stage complication of this disease is oligoarticular arthritis, often involving the knee. In ∼10% of cases, arthritis persists after appropriate antibiotic treatment, leading to a proliferative synovitis typical of chronic inflammatory arthritides. Here, we provide evidence that peptidoglycan (PG), a major component of the cell envelope, may contribute to the development and persistence of Lyme arthritis (LA). We show that has a chemically atypical PG (PG) that is not recycled during cell-wall turnover. Instead, this pathogen sheds PG fragments into its environment during growth. Patients with LA mount a specific immunoglobulin G response against PG, which is significantly higher in the synovial fluid than in the serum of the same patient. We also detect PG in 94% of synovial fluid samples (32 of 34) from patients with LA, many of whom had undergone oral and intravenous antibiotic treatment. These same synovial fluid samples contain proinflammatory cytokines, similar to those produced by human peripheral blood mononuclear cells stimulated with PG In addition, systemic administration of PG in BALB/c mice elicits acute arthritis. Altogether, our study identifies PG as a likely contributor to inflammatory responses in LA. Persistence of this antigen in the joint may contribute to synovitis after antibiotics eradicate the pathogen. Furthermore, our finding that sheds immunogenic PG fragments during growth suggests a potential role for PG in the immunopathogenesis of other Lyme disease manifestations.