Role of mast cells in the pathogenesis of rheumatoid arthritis

ABSTRACT

To elucidate the involvement of mast cells in the pathogenesis of rheumatoid arthritis [RA] by finding out the cells in synovial tissue and their products in the synovial fluid. Also, by studying the ultrastructure of mast cells, in an attempt to throw light on possible new strategies in the management of this disease. Twenty RA patients and ten subjects with acute post traumatic knee effusion- who served as a control group- were recruited for this study. All synovial fluid [SF] samples were investigated for mast cell products tryptase and histamine using radioimmunoassay [RIA]. Synovial tissue [ST] specimens were obtained from control subjects and RA patients. These specimens were stained with hematoxylin and eosin for assessment of lymphocytic infiltration and with the conventional mast cell stain "Toluidine blue". A study of the ultrastructure of synovial tissue specimens was done to further document changes of synovial mast cells. SF tryptase and histamine were highly significantly raised in RA patients in contrast to control subjects [p<0.001]. There was a statistically significant increase in ST mast cell scoring in rheumatoid synovium as compared to that of control subjects [p<0.01]. Ultrastructural study of rheumatoid synovial tissue revealed evidence of degranulation of some mast cells. There was a highly significant positive correlation between ST mast cell score, SF tryptase, SF histamine and the modified disease activity score [DAS] as well as with the severity of the disease as assessed by Larsen score [p<0.001]. A highly significant positive correlation was found between ST mast cell scoring and the histological inflammatory index [p< 0.001]. Mast cells are an important contributor of the rheumatoid process in synovium reflecting its role in disease activity and joint destruction. These findings might have important implications for understanding the pathogenesis of RA. Hence, drug therapy targeting mast cells may have a role in controlling the activity and severity of the disease