INFILTRATES OF ACTIVATED MAST-CELLS AT THE SITE OF CORONARY ATHEROMATOUS EROSION OR RUPTURE IN MYOCARDIAL-INFARCTION

Background Erosion and rupture of coronary atheromas are the events pr eceding the vast majority of acute coronary syndromes. The shoulder re gions of atheromas, the sites at which erosion or rupture is most like ly to occur, are the sites at which mast cells accumulate. These cells are filled with neutral proteases capable of triggering extracellular matrix degradation via activation of matrix metalloproteinases. To ob tain more direct evidence for the participation of mast cells in the a cute coronary syndromes, we quantified the numbers of mast cells at er oded or ruptured sites of coronary atheromas in patients who died of m yocardial infarction. Methods and Results In specimens of coronary art eries from 20 patients who had died of acute myocardial infarction, th e site of atheromatous erosion or rupture was identified. The specimen s were stained with monoclonal antibodies against the two major protea ses of mast cells, tryptase and chymase, and against macrophages, T ly mphocytes, and smooth muscle cells. At the immediate site of erosion o r rupture, mast cells amounted to 6% of all nucleated cells, in the ad jacent atheromatous area to 1%, and in the unaffected intimal area to 0.1%. The proportions of these mast cells that were activated, ie, had been stimulated to degranulate and release some of their tryptase and chymase contents, were 86% at the site of erosion or rupture, 63% in the adjacent atheromatous area, and 27% in the unaffected intima. At t he site of erosion or rupture, the numbers of macrophages and T lympho cytes were also increased, but the number of smooth muscle cells was d ecreased. Conclusions The accumulation of activated mast cells (200-fo ld more than in the unaffected coronary intima) at the site of atherom atous erosion or rupture suggests that in thrombotic coronary occlusio n the role played by mast cells is significant.