[Macrophages in rheumatoid synovial membrane: an update]

Area of Science:

• Immunology
• Rheumatology
• Cell Biology

Background:

• Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovial joint inflammation.
• Mononuclear phagocytes (MPs) are key immune cells implicated in inflammatory processes.
• The specific role and phenotype of MPs in RA pathogenesis require further elucidation.

Purpose of the Study:

• To investigate the immunophenotype of synovial lining and subintimal mononuclear phagocytes (MPs) in rheumatoid arthritis (RA).
• To compare the phenotype of MPs in RA with those in osteoarthritis (OA) to understand their significance in RA pathobiology.

Main Methods:

• Immunohistology was employed to analyze the expression of various cell surface antigens on synovial MPs.
• Antibodies were used to detect macrophage-associated antigens, cell adhesion molecules, and activation markers.
• The immunophenotype of MPs in RA synovial tissue was compared with that in OA synovial tissue.

Main Results:

• In RA, lining synovial cells (SLCs) were predominantly MPs (80-90%), as were cells in the subintima (50-70%).
• RA synovial MPs displayed a broad range of macrophage-associated antigens and cell adhesion molecules, with increased expression of activation and maturation markers compared to OA.
• The monocyte marker CD14 was downregulated on SLCs in both RA and OA, and CD68 was found to be an unreliable macrophage marker in OA intima.

Conclusions:

• Synovial MPs are highly activated and play a central role in RA pathogenesis.
• The recruitment of these activated MPs in RA is independent of lymphocyte infiltration.
• Understanding the immunophenotype of synovial MPs offers insights into RA pathobiology and potential therapeutic targets.