Human synovial fibroblasts and CD4 T cells cooperate to promote inflammation in the RA synovial joint
Andreea Petrasca (1), Grainne Jameson (1), Trudy McGarry (2), Douglas J Veale (3), Ursula Fearon (2,3) and Jean M Fletcher (1, 2)
1. School of Biochemistry & Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Ireland, 2. School of Medicine, Trinity Biomedical Sciences Institute, Trinity College Dublin, Ireland, 3. Rheumatology, St. Vincent’s University Hospital, Dublin, Ireland
Rheumatoid arthritis (RA) is a chronic autoimmune disease characterised by synovial tissue proliferation and degradation of articular cartilage. Activated synovial fibroblasts proliferate and express matrix-degrading proteases, adhesion molecules and proinflammatory cytokines, which contribute to cartilage and joint destruction. Moreover, synovial cell activation correlates with infiltration of inflammatory lymphocytes and monocytes which in turn contribute to synoviocyte activation, thus further exacerbating inflammation.
The functional relationship linking fibroblasts and T lymphocytes in this complex microenvironment has yet to be characterised. Therefore, we established an in vitro model to examine the outcomes of co-culturing activated human CD4 T cells with RA synovial fibroblasts.
Co-culture assays were carried out using synovial fibroblast cells derived from arthroscopy biopsies of RA patients or immortalised K4 synovial fibroblasts. Human CD4 T cells were stained with a proliferation-tracking dye, stimulated and co-cultured with synovial fibroblasts for 5 days. The resulting cell cultures and supernatants were examined for proliferation, cytokine production, secretion of matrix metalloproteinases and expression of adhesion molecules. Furthermore, we investigated the invasive and migrative potential of synovial fibroblasts cultured with CD4 T cell conditioned medium.
We found that CD4 T cells and synovial fibroblasts reciprocally induced an increased expression of adhesion molecules ICAM and VCAM. In addition, we saw that factors secreted by activated CD4 T cells increased the migrative and invasive capability of synoviocytes. Furthermore, co-culture of CD4 T cells and synovial fibroblasts resulted in proliferation of CD4 T cells expressing increased levels of the proinflammatory cytokines IFN-γ and IL-17a and RANKL, and an increase in secretion of IL-6, IL-8, IFN-γ and IL-17a and matrix metalloproteinases MMP-1 and MMP-3 from the co-cultures. Lastly, we demonstrate that these changes in pro-inflammatory profiles are linked with alterations in metabolism.
These results indicate that CD4 T cells work mutually with synoviocytes to create an inflammatory microenvironment likely to promote joint destruction through a milieu of proinflammatory cytokines and increased adhesiveness and invasiveness of synovial cells.