Tissue factor expression in rheumatoid synovium: a potential role in pannus invasion of rheumatoid arthritis

Angiogenesis, as well as pannus formation within the joint, plays an important role in the erosion of articular cartilage and bone in the pathological process of rheumatoid arthritis (RA). Tissue factor (TF), an essential initiator of the extrinsic pathway of blood coagulation, is also involved in the angiogenesis and the pannus formation of RA progression. In the present study, we used immunofluorescence and confocal scanning methods to characterize TF immunolocalization in RA synovium. We showed that positive staining of TF could be immunolocalized in synoviocytes, CD19⁺ B cells and CD68⁺ macrophages, whereas weak or negative staining of tissue factor could be found in CD34⁺ endothelial cells of neo-vessels, CD3⁺ T cells and CD14⁺ monocytes in RA synovium tissues. Our study demonstrates a detailed local expression of TF in the rheumatoid synovium, and supports the notion that TF, expressed not only by the synoviocytes themselves, but also the infiltrating CD19⁺ B cells and CD68⁺ macrophages, is involved in the pannus invasion in the progression of rheumatoid arthritis.