Mechanisms to facilitate the development of autoimmune arthritis by over-expression of HTLV-1pX.

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We generated a double-mutant mouse by crossing two murine models of RA, a gp 130 mutant knock-in mouse (gp130^<F759/F759>) and an HTLV-1 pX transgenic mouse (pX-Tg), in a C57BL/6 background, which is resistant to arthritis. The mice spontaneously developed severe arthritis with a much earlier onset than the gp130^<F759/F759> mice and with a much higher incidence than did the pX-Tg mice. The symptoms of gp130^<F759/F759> mice, including lymphoadenopathy, splenomegaly, hyper-γ-globulinemia, autoantibody production, increases in memory/activated T cells and granulocytes in the peripheral lymphoid organs, and a decrease in the class II MHC^<bright> CD11c^+ population, were augmented in the double mutants. Immunohistochemical analyses revealed production of IL-6 and nuclear translocation of phospho-STAT3 in the macrophages and fibroblasts in the synovium of arthritic joints. CD4^+ T cells are closely located to the class II MHC molecules expressed by CD11b^+ cells in the synovium. Marked reductions in incidence, severity, and immunological abnormalities were seen in the triple mutant, IL-6^<-/->/gp130^<F759/F759>/pX-Tg, indicating that the arthritis in the double mutant is IL-6 dependent. Inhibitory effects on the maturation of dendritic cells by IL-6/STAT3 signal were demonstrated in vivo and in vitro. Experiments of bone marrow transfer revealed that both the gp130^<F759/F759> mutation and over-expression of pX gene in the non-hematopoietic cells but not in hematopoietic cells are required for the development of arthritis.