Grafting of Fibroblasts Isolated from the Synovial Membrane of Rheumatoid Arthritis (RA) Patients Induces Chronic Arthritis in SCID Mice—A Novel Model for Studying the Arthritogenic Role of RA Fibroblasts

The objective of this study was to verify whether isolated rheumatoid arthritis (RA) synovial fibroblasts induce chronic arthritis in SCID mice, in analogy to whole tissue pieces. Fibroblasts were isolated from the synovial membrane of four RA patients (or controls) by out-growth and repeated-passage culture. Following flow-cytometry characterization, 2×106cells were transferred into the left knee joint of SCID mice. The development of arthritis was assessed by joint swelling and histological changes. Human and murine cytokines were measured in vitro in co-cultures (or Transwell™ systems) of human and murine cells. Purified RA synovial fibroblasts, but not healthy synovial or skin fibroblasts, induced hu/mu arthritis within 6 weeks. In-vitro secretion of murine and human interleukin(IL)-6, as well as murine tumour necrosis factor (TNF)-α, indicated cross-activation between murine macrophages and human RA fibroblasts. Soluble-factor mechanisms proved more effective than cell-contact mechanisms. Purified RA fibroblasts can, alone, induce hu/mu SCID arthritis. The cytokine profile suggests that xenogeneic interaction between human fibroblasts and murine macrophages may determine the sequence of events leading to hu/mu arthritis.