Immunofluorescence reveals the presence of autoantibodies in OA sera. Cryosections of synovial membranes were incubated with control (A) or OA (B) sera. The binding of autoantibodies was detected via FITC-labeled anti human IgG antibodies (green). Fibroblasts were stained with the specific antibody (5B5) and developed via SA-rhodamine (red). Nuclei are counterstained using DAPI (blue).