Increased expression of HLA-DQ antigens by interstitial cells and endothelium in the synovial membrane of rheumatoid arthritis patients compared with reactive arthritis patients.

We investigated cellular phenotypes and expression of class II major histocompatibility complex antigens on endothelium and cellular infiltrates in synovium from patients with rheumatoid arthritis (RA) or reactive arthritis, using an indirect immunoperoxidase technique. The RA specimens showed synovial lining layer hypertrophy and several focal accumulations of lymphocytes, both of which were absent in the reactive arthritis synovium. The percentage of cells expressing monocyte/macrophage markers was significantly higher in RA specimens. The percentages of cells expressing B and T cell markers were similar in both diseases. There was no significant difference in the expression of HLA-DR or DP by endothelium in the 2 diseases, but a marked increase in expression of HLA-DQ by endothelium was observed in the RA synovium versus that from patients with reactive arthritis. This overexpression of HLA-DQ was also seen in the interstitial cells of RA patients compared with reactive arthritis patients. In the reactive arthritis synovium, a significant population of cells (30%) was noted to be HLA-DR positive, and negative for macrophage and lymphocyte markers. Some of these cells had a dendritic morphology. The coexpression of HLA-DQ and HLA-DR may play an important role in antigen presentation and disease chronicity in RA.