Interleukin-1 lymphocyte chemotactic activity in rheumatoid arthritis synovial fluid

We examined the role of interleukin-1 (IL-1) in the chemotactic activity of rheumatoid arthritis (RA) synovial fluid (SF). Crude RA SF was found to be chemotactic for B cells and T cells. After AcA 54 gel filtration, the principal peaks of chemotactic activity were found in the 5-kd, 16-kd, and 60-kd fractions. The majority of the chemotactic activity for both the B cells (74-85%) and the T cells (69-78%) was removed from these fractions by treatment with anti-IL-1 antibody. However, in crude SF, approximately 60% of the chemotactic activity for B cells and 40% of that for T cells was removed, indicating the presence of additional chemotactic factors in RA SF. IL-1 activity, measured by the thymocyte proliferation assay, was demonstrated in RA SF AcA 54 Ultrogel fractions after separation from inhibitors of thymocyte proliferation that are present in crude SF. On chromatofocusing of the 16-kd fraction, the principal peaks of both thymocyte proliferation activity and chemotactic activity were present in the same fractions with pI values of 6.8, 5.7, and 5.2, which are characteristic of IL-1. The demonstration of IL-1-associated chemotactic activity in RA SF may reflect the presence in the RA synovial membrane (including both the lining layer and the subsynovial layer) of activated macrophages, interstitial histiocytic cells, and other IL-1-producing cells, such as endothelial cells. These findings suggest that such cells may attract lymphocytes to their environment by secretion of IL-1.