DISTRIBUTION, ACTIVATION AND TRYPTASE CHYMASE PHENOTYPE OF MAST-CELLSIN THE RHEUMATOID LESION

Objective-To determine the distribution, activation, and tryptase/chym ase phenotype of mast cells (MCs) in the rheumatoid lesion. Methods-MC tryptase and chymase were studied by immunohistochemistry using monoc lonal antibodies and examination by brightfieid, interference, and flu orescent microscopy. Thirty four specimens of cartilage-pannus junctio n and 26 specimens of rheumatoid synovium, all derived from knee surge ry, were examined. Results-MCs were identified in all specimens examin ed, but their distribution and local concentrations varied, both withi n and between specimens. As a proportion of total synovial cells, ther e were more MCs in fibrous synovial tissues than in those with active inflammatory cell infiltrations; MCs usually showed a peripheral distr ibution around lymphocytic/mononuclear cell infiltrations. Most cartil age-pannus specimens demonstrated local concentrations of MCs at, or c lose to, sites of cartilage erosion, a significant proportion of which showed extracellular tryptase indicative of MC degranulation. MC degr anulation was often associated with localised oedema and disruption of the stromal matrix. Two MG phenotypes were identified: one population contained tryptase alone (MC(T)) whilst another contained both trypta se and chymase (MC(TC)). The ratio MC(T):MC(TC) approximated 8:1. Conc lusions-This histological study demonstrated that local concentrations of MCs and their activation/degranulation are commonly observed in th e rheumatoid lesion, and especially at sites of cartilage erosion. Suc h observations add weight to the concept that MCs contribute to the pr ocesses of inflammation, matrix degradation and tissue remodelling.