Infiltration of hypertrophic esophageal smooth muscle by mast cells and basophils

Partial obstruction leads to chronic distension and muscular hypertrophy of the opossum esophagus. The smooth muscle cells of the circular muscle layer enlarge, become pleomorphic and are surrounded by an amorphous ground substance in the extracellular space. Here we describe the histological and ultrastructural features of a peculiar cellular infiltrate in the hypertrophic smooth muscle. The infiltrate consisted uniquely of mast cells and basophils. In per unit area, the number of mast cells increased from 0.9 +/- 0.1 cells in controls to 3.7 +/- 0.2 in hypertrophic smooth muscle; the corresponding numbers for basophils were 2.5 +/- 0.2 and 7.2 +/- 0.3 cells. Cells were seen primarily in the septal spaces of the circular muscle layer and at the interface of the circular and longitudinal muscle layer. The cytoplasm of basophils is normally packed with round and oval granules. The granules stain metachromatically and with varying intensity on Wright-Giemsa stains. On transmission electronmicroscopy, granules display a membrane and a great diversity in the structure of their luminal contents. In hypertrophic muscle, most granules were discharging their contents into the cytoplasm or extracellular space. The membranes of adjacent empty granules then fused to form a chain of vacuoles. Similar changes occurred also in the mast cells which differed from the basophil by their lack of nuclear lobulation and by the greater homogeneity of their cytoplasmic granules. It is possible that these inflammatory cells are involved in the reconstruction of the smooth muscle and its connective tissue which occur during esophageal distension and hypertrophy.