Background: The rheumatoid arthritis (RA) joint is characterized by an inflammatory synovial pannus which mediates tissue destruction. Interleukin (IL)-4 reduces the production of many proinflammatory cytokines, particularly by activated macrophages. Therefore, we examined the ability of adenovirally delivered IL-4 for the treatment of human RA to reduce the secretion of proinflammatory molecules.
Methods: Adenoviral vectors encoding the genes for human IL-4 (AxCAIL-4) and bacterial beta-galactosidase (AxCAlacZ) were generated and examined for appropriate production and biological activity. RA synovial tissue (ST) explants or fibroblasts were infected with AxCAIL-4 or a beta-galactosidase producing vector, as a control, and conditioned medium (CM) was collected for ELISA analysis.
Results: AxCAIL-4 decreased the production of the inflammatory cytokines IL-1 beta and tumor necrosis factor-alpha in RA ST explant CM. IL-8 levels were significantly reduced by 71%, 88%, and 82% at 24, 48, and 72 hours, respectively, in RA ST explant CM. In the same CM, monocyte chemotactic protein-1 (MCP-1) levels decreased 60% at 48 hours. In contrast, RA synovial fibroblast CM levels of MCP-1 were increased by AxCAIL-4. Epithelial neutrophil activating peptide-78 levels produced by RA ST explants were significantly decreased by AxCAIL-4 by 88%, 92%, and 93% at 24, 48, and 72 hours, respectively. Growth related gene product-alpha levels were likewise decreased in RA ST explant CM. In ST explants as well as RA synovial fibroblasts, IL-4 treatment decreased prostaglandin E2 (PGE2) production.
Conclusions: Increased expression of IL-4 via gene therapy may decrease RA-associated inflammation by reducing proinflammatory cytokines and PGE2.