[Macrophages in rheumatoid synovial membrane: an update]

Abstract

The immunophenotype of lining and subintimal synovial mononuclear phagocytes (MP) of rheumatoid arthritis (RA) were sought by immunohistology and compared with osteoarthritis (OA) tissue in order to determine the significance of MPs in the pathobiology of RA. Almost all the lining cells (SLCs) in RA consisted of MPs (80 to 90% expressing CD45/CD14/CD68). A major proportion of the interaggregate areas of the rheumatoid subintima was also made of MP cells (50 to 70% expressing CD14/CD68). A marked variation in the immunohistological reaction of antibodies reacting within intimal MPs and between intimal and subintimal MPs was found. Intimal MPs expressed a wide range of macrophage-associated antigens, including receptors for Fc (CD16, CD32, CD64) and complement (CD35, CD11b, CD11c) as well as several integrin and non-integrin cell adhesion molecules (CD29/CD49b, CD49d, CD49f, CD51/CD61, CD11a, CD31, CD54, CD44, CD9, CD63). The monocyte marker, CD14, was down-regulated on SLCs in both RA and OA. When compared to intimal expression of leucocyte common antigen (CD45), CD68, a pan-macrophage maturation antigen, was found to be an unreliable macrophage antigen in OA intima. There was no difference in antigenic phenotype of SLCs in inflammatory and non-inflammatory OA with early activation markers (CD25, CD71) mainly present on MPs. In RA, synovial MPs showed increased expression of activation, maturation and functional antigens suggesting that they are rapidly and fully activated. The fact that their recruitment was independent of the degree of lymphocyte infiltration further emphasises the central importance of synovial MPs in RA.