Tissue Outgrowth in Patients with Rheumatoid Arthritis

BACKGROUND: The aim of this study was to analyze cellular and cytokine (an immunoregulatory substance secreted by cells of the immune system) interactions governing the development of synovial tissue (cushions and lines the joints) outgrowth in patients with rheumatoid arthritis (RA).

METHODS: A single-cell suspension of dissociated synovial tissues of RA patients was cultured for a long period to develop tissue outgrowth. The resulting tissue outgrowth was characterized by immunohistochemical staining and ELISA.

RESULTS: The tissue outgrowth developed in vitro included various cell types, such as macrophage-like synovial cells (functions to protect the body by consuming foreign bodies), fibroblast-like (gives rise to connective tissue) synovial cells and lymphocytes (lymph cell). Even after prolonged cultivation, synovial cells devoid of infiltrating T lymphocytes did not form tissue outgrowth. The outgrowth contained CD3+ cells, LeuM3 (CD14)+ cells and HLA-DR+ cells. The T cells expressed lymphocyte function-associated antigen (LFA)-1 and CD2, and the synovial cells expressed intracellular adhesion molecule (ICAM)-1 and LFA-3, suggesting possible interactions via LFA-1/ICAM-1 and CD2/LFA-3. Production of T-cell derived IFN-gamma and IL-17 and synovial-cell-derived fibroblast growth factor (FGF)-1 and IL-15 was confirmed in the tissue outgrowth as well as in RA synovial tissue. These cell types stimulate each other by secreting cytokines, leading to the secretion of proinflammatory cytokines and matrix metalloproteinase (MMP)-1 by the tissue outgrowth and proliferation of both lymphocytes and synovial cells.

CONCLUSION: This study emphasizes the importance of cellular interactions between T cells and synovial cells, via adhesion molecules and the secretion of cytokines with stimulatory activity towards other cell types, for the hyperactivity of RA synovial cells.

Source: Int Arch Allergy Immunol 2000 Jan;121(1):68-79.

Merriam Webster’s Medical Desk Dictionary. Merriam-Webster Inc. Publishers.

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