Annexin A2 is a target of autoimmune T and B cell responses associated with synovial fibroblast proliferation in patients with antibiotic-refractory Lyme arthritis.

In this study, autoantibody responses to annexin A2 were found in 11-15% of 278 patients with Lyme disease, including in those with erythema migrans (EM), an early sign of the illness, and in those with antibiotic-responsive or antibiotic-refractory Lyme arthritis (LA), a late disease manifestation. In contrast, robust T cell reactivity to annexin A2 peptides was found only in patients with responsive or refractory LA. In LA patients, annexin A2 protein levels, which were higher in the refractory group, correlated with annexin A2 antibody levels in sera and synovial fluid. In addition, in patients with antibiotic-refractory LA who had anti-annexin A2 antibodies, synovial tissue had intense staining for annexin A2 protein, greater synovial fibroblast proliferation and more tissue fibrosis. Thus, a subset of LA patients had T and B cell responses to annexin A2, and in the refractory group, annexin A2 autoantibodies were associated with specific pathologic findings.