Accumulation of activated mast cells in the shoulder region of human coronary atheroma, the predilection site of atheromatous rupture.

BACKGROUND Rupture in the shoulder region of a coronary atheroma is considered to be a sequel to local extracellular matrix degradation in this highly vulnerable site. Such degradation could be triggered by mast cells, which are filled with neutral proteases and are present in coronary atheromas. However, the distribution and phenotype of mast cells within coronary atheromas have not been studied. METHODS AND RESULTS Specimens of normal and atherosclerotic human coronary intima from 32 autopsy cases with ages ranging from 13 to 67 years were stained with monoclonal antibodies against the two major proteases of mast cells, tryptase and chymase. Of the tryptase-containing mast cells, a variable proportion (average, 40%; range, 0% to 100%) also contained chymase. In the normal coronary intimas, mast cells amounted to 0.1% of all nucleated cells. In the fatty streaks, this proportion was higher by 9-fold, and in the cap, core, and shoulder regions of atheromas by 5-, 5-, and 10-fold, respectively. Electron and light microscopic studies of mast cells in the shoulder region of atheromas revealed degranulation of mast cells, a sign of their activation, and moreover, that the proportion of activated mast cells was much higher (85%) in this region than in the normal intima (18%). CONCLUSIONS The far higher proportion (50-fold) of activated mast cells in the shoulder region of atheromas supports the hypothesis that mast cells, a cell type capable of triggering matrix degradation, actively participate in the destabilization and ensuing rupture of coronary atheromas and thus may trigger an acute coronary event.