Effects of the neuropeptide, substance P, on lymphocyte proliferation in rheumatoid arthritis

There is evidence supporting the involvement of the neuropeptide, substance P, in the pathogenesis of rheumatoid arthritis. In view of the suggested role of T-cells in this disease, we have investigated the effects of substance P on mitogen-induced lymphocyte proliferation in rheumatoid arthritis patients. The peripheral blood mononuclear cells from 20 patients with rheumatoid arthritis and 25 controls were cultured in the presence or absence of substance P (10(-10) M to 10(-6) M) and stimulated with phytohaemagglutinin or concanavalin A. After 3 days of culture the proliferative responses were determined by measuring [3H]thymidine incorporation into the cells. Substance P enhanced, in a dose-dependent manner, the lymphocyte proliferative responses both in rheumatoid arthritis patients and in controls. Although there was a trend towards a greater enhancing effect in the rheumatoid arthritis patients, this was not statistically significant. Some individual patients with rheumatoid arthritis showed enhancements of lymphocyte proliferation with substance P that were clearly outside the range seen in healthy controls. The possibility that substance P has a role in the pathogenesis of rheumatoid arthritis through the up-regulation of lymphocyte activation should be considered in further studies of the immunomodulatory properties of substance P in arthritis.