Vascular endothelial growth factor expression by activated synovial leukocytes in rheumatoid arthritis - Critical involvement of the interaction withsynovial fibroblasts

Objective. To examine the expression and regulation of the angiogenic facto r, vascular endothelial growth factor (VEGF), by fibroblast-like synoviocyt es (FLS), monocytes, and polymorphonuclear neutrophils (PMNs) isolated from the synovial fluid (SF) of rheumatoid arthritis (RA) patients. Methods. Monocytes or PMNs obtained from RA SF were cocultured with unstimu lated, semiconfluent RA FLS. Culture supernatants were assayed for the prol iferation and in vitro tube formation of endothelial cells, and for the pro duction of VEGF, by enzyme-linked immunosorbent assay. The expression of VE GF messenger RNA and protein was also determined by reverse transcription-p olymerase chain reaction and immunohistochemistry, respectively. Results. We found that the interaction of inflammatory, activated leukocyte s with FLS resulted in synergistic increases in VEGF expression and secreti on, which contributed to the proliferation of endothelial cells and to in v itro endothelial tube formation. The induction of VEGF was mediated via spe cific adhesion molecules, as indicated by the finding that anti-integrin an tibodies significantly inhibited VEGF. Furthermore, the levels of VEGF secr etion correlated with the expression of cell surface integrin (CD11b and CD 18) on both monocytes and PMNs in the SF. Conclusion. VEGF expression within inflamed joints thus appears to be regul ated not only by inflammatory cytokines, but also by the physical interacti on of activated leukocytes and FLS. Once expressed, VEGF likely plays a cru cial role in the neovascularization of the pannus and the progressive joint destruction associated with the synovial inflammation of RA.