Nerve growth factor (NGF) autoantibodies and NGF in the synovial fluid: implications in spondylarthropathies

We investigated the presence of nerve growth factor (NGF) autoantibodies and NGF in the synovial fluid (SF) of patients with different forms of chronic arthritis such as spondylarthropathy (SpA), rheumatoid arthritis (RA), calcium pyrophosphate dihydrate crystal deposition disease (CPPD) and osteoarthritis (OA) and compared them to their levels in serum. NGF autoantibodies were detected by ELISA and by their capacity to immunoprecipitate NGF and to inhibit its biological activity. NGF was measured with a two-site enzyme-linked immunosorbent assay. Significantly high NGF autoantibody levels (p < 10(-4)) and high frequency of detectable NGF (p < 0.01) were observed in the SF of SpA patients and to a lesser degree in RA patients as compared to CPPD and OA patients. In the serum high frequency of detectable NGF was observed only in RA patients. These results suggest a role of NGF autoantibodies and NGF in joint inflammation especially in spondylarthropathies.