The stichosome and its secretion granules in the mature muscle larva of Trichinella spiralis.

The stichosome of the mature muscle larva of Trichinella spiralis consists of a single row of 45 to 55 stichocytes. Each stichocyte is about 25 mum in diameter and possesses a single nucleus. A duct leads from each stichocyte to the lumen of the esophagus. The stichocyte cytoplasm contains mitochondria, structures resembling Golgi-complexes, rough endoplasmic reticulum, and usually 1 of 2 types of secretory granules. The alpha-granule measures about 800 mn in diameter, contains a prominent inclusion, and has a granular matrix. The beta-granule is about 600 mn in diameter and is homogeneous in appearance. Both granule types are surrounded by a single membrane. Ten to thirteen stichocytes containing alpha-granules are confined to the posterior portion of the stichosome. After isopycnic centrifugation in sucrose gradient of large granule fractions obtained from cell-free homogenates, the alpha- and beta-granules show characteristic distribution patterns as revealed by the morphology of the fractions. The median equilibrium density of the alpha-granules is 1.245, while that of the beta-granules is 1.230. There is a correlation between the distribution of the granules and of antigens reacting with hyperimmune antitrichinella seruma. At least 4 unique antigens can be attributed to each of the granule types. Fractions enriched in mitochondria do not contain specific antigens. Antigens from both types of secretory granules cross react totally with those present in the excretion-secretion products of living muscle larvae. Cytoimmunochemical data show that antigens are distributed in a patchy fashion throughout the stichocyte cytoplasm. This finding is consistent with the distribution of the secretory granules in the intact stichocyte.