Low-level production of interleukin-13 in synovial fluid and tissue from patients with arthritis

Rheumatoid arthritis (RA) is a chronic, aggressive disease characterized by inflammatory cells in the synovial tissue (ST) and synovial fluid (SF), Interleukin (IL)-13 inhibits the production of proinflammatory cytokines, chemokines, and hematopoietic growth factors by activated human monocytes. The aim of this study was to determine the production of IL-13 in various forms of arthritis. The presence of IL-13 in RA was found to be low, in that 18 of 26 RA SF samples and 10 of 14 RA peripheral blood (PB) samples had nondetectable levels (less than or equal to 12 pg/ml), Similar low levels were found in SF and PB from patients with osteoarthritis (OA) and other arthritides, In contrast, RANTES, IL-8, monocyte chemotactic protein-1, and soluble P-selectin were found at levels of 13-, 120-, 1200-, and 2000-fold excess of IL-13, respectively, Mononuclear cells isolated from RA SFs did not produce significant levels of IL-13 in culture (less than or equal to 12 pg/ml) but were able to do so when stimulated with phytohemagglutinin. Likewise, tissue explants from RA synovium cultured for 24 or 48 hr with or without serum did not produce appreciable quantities of IL-13 (less than or equal to 12 pg/ml), Immunohistochemical data were in accordance with this result in that antigenic IL-13 was not detected on the majority of RA, OA, and normal (NL) ST cells, These results demonstrate a paucity of IL-13 within the joints of RA, OA, NL, and other arthritic patients by comparison with levels of Other cytokines. (C) 1997 Academic Press.