OBJECTIVES--To examine the distribution and activation of mast cells (MCs) in the rheumatoid lesion (cartilage-pannus junctions demonstrating cartilage erosion), and to determine whether or not their tissue distribution is related to that for tumour necrosis factor alpha (TNF alpha), interleukin-1 (IL-1), stromelysin-1, and collagenase. METHODS--Immunolocalisation of MC-tryptase was used to identify MCs and their states of degranulation in 35 specimens of cartilage-pannus junctions. Dual immunolocalisation techniques using alkaline phosphatase and peroxidase conjugated antibodies were used to compare the distributions of MCs with the proinflammatory cytokines TNF alpha and IL-1, and the cartilage or matrix degrading enzymes stromelysin-1 and collagenase. RESULTS--Stromelysin-1, TNF alpha, and IL-1 beta were especially prominent at the cartilage-pannus junctions, albeit with patchy distributions. Extracellular MC tryptase, indicative of MC activation/degranulation, was commonly observed at sites of cartilage erosion, and was often associated with the microenvironmental expression of TNF alpha, IL-1 beta, stromelysin-1, and collagenase. Such observations were often associated with localised sites of tissue oedema and stromal disruption. CONCLUSION--MC activation was frequently associated with proinflammatory cytokine and metalloproteinase expression by neighbouring cells, thereby suggesting an important contributory role for the MC in mediating matrix degradation and oedematous changes within microfoci of the rheumatoid lesion.
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