Molecular cloning and sequence of porcine interleukin 6 cDNA and expression of mRNA in synovial fibroblasts in vitro.

Synovial fibroblasts, derived from enzyme digestion of porcine synovial tissue, released interleukin 6 (IL-6) bioactivity in culture and this release was enhanced by IL-1 alpha. The porcine IL-6 was cloned from a cDNA library made from these cells using human IL-6 cDNA as a probe. Clone PIL-6[13-8] was sequenced and coded for 212 amino acids with 62% homology and 42% homology to published sequences of human and mouse (or rat), respectively. The cDNA was used to probe the expression of pig IL-6 at the RNA level in pig synovial fibroblasts in vitro. IL-1 alpha and tumor necrosis factor markedly induced steady state levels of IL-6 at 20 h in serum-free conditions, whereas transforming growth factor-beta (TGF-beta), epidermal growth factor, and 10% fetal calf serum did not. TGF-beta pretreatment dramatically inhibited TNF-induction of the IL-6 mRNA but did not markedly affect induction by IL-1 alpha. However, TGF-beta did reduce IL-6 activity detected in the supernatants of IL-1-induced cells.