Reduced synovial membrane macrophage numbers, elam‐1 expression, and lining layer hyperplasia in psoriatic arthritis as compared with rheumatoid arthritis

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Abstract
Objective. To define the immunohistologic features of the synovial membrane (SM) of patients with psoriatic arthritis (PA) and to compare them with those of an age‐ and disease‐duration–matched population of patients with rheumatoid arthritis (RA). Methods. Synovial membrane needle biopsy was performed on 15 PA patients with knee involvement (8 had asymmetric oligoarthritis and 7 had symmetric polyarthritis) and on 15 RA controls. Specimens were stained with monoclonal antibodies against T cells (CD3, CD8, CD4, CD45RO), B cells (CD20), macrophages (Mac387, CD14), and cells bearing class II antigens (DAKO‐DR). Vascular endothelium was examined using a polyclonal antibody to Factor VIII–related antigen, and adhesion molecule expression was examined using antibodies 1.3B6, 6.5B5, and 1.4C3, which identify endothelial leukocyte adhesion molecule 1 (ELAM‐1), intercellular adhesion molecule 1 (ICAM‐1), and vascular cell adhesion molecule 1 (VCAM‐1), respectively. Results. There was significantly less lining layer hyperplasia, fewer macrophages, and a greater number of blood vessels in PA SM than in RA SM. ELAM‐1 expression was less intense in PA than in RA SM, while there was no difference in expression of ICAM‐1 and VCAM‐1. Numbers of B cells, T cells, and T cell subsets (predominantly CD4, CD45RO T cells) were similar in both groups of patients. Conclusion. Our findings demonstrate important differences in the immunohistologic features of PA and RA SM. The PA SM is more vascular, ELAM‐1 expression is less intense, and fewer macrophages invade the stroma and migrate to the lining layer than in RA SM. However, the lymphocytic infiltrate in the SM of both groups is similar.