In situ hybridization of IL-6 in rheumatoid arthritis

Abstract

IL-6, an important mediator of the acute phase response, has been implicated in the pathogenesis of rheumatoid arthritis (RA). Many cell types including macrophages, T cells, B cells, endothelial cells and fibroblasts can produce this cytokine and production is largely regulated at the level of gene transcription or mRN A stabilization. In this paper we have first measured the levels of IL-6 activity in synovial fluid (SF) and serum from patients with RA and then localized IL-6-producing cells in the synovium by in situ hybridization combined with immunophenotyping. Patients with RA had raised levels of IL-6 in both SF and serum compared with patients with osteoarthritis and age-matched healthy controls. In individual RA patients tested serially after admission to hospital, serum IL-6 was initially raised and, unexpectedly, increased with clinical improvement, In situ hybridization of IL-6 mRNA showed positive cells both in the lymphocyte-rich aggregates and adjacent to small blood vessels. With immunophenotyping it was found that cells containing IL-6 mRNA were often in contact with CD14⁺ tissue macrophages and double immunophenotyping revealed that immunoreactive IL-6 was often associated with synovial T cells.