Mast cells in the gills and intestines of naturally infected fish: evidence of migration and degranulation.

Immunopathological and ultrastructural studies were carried out on the gills of bream, Abramis brama, naturally infected with the copepod Ergasilus sieboldi and on the intestine of brown trout, Salmo trutta, infected with the acanthocephalan Echinorhynchus truttae. Infected gills showed extensive tissue damage due to copepod attachment, including hyperplasia, as well as proliferation of mast cells, rodlet cells and mucous cells. In parasitized gills of bream, mast cells were more abundant than in uninfected gills. They were free within the lacunae, as well as outside and inside the blood vessels of the primary lamellae, and made intimate contact with vascular endothelial cells and with neutrophils. In some infected gills, degranulation of mast cells was common. Infected intestines of brown trout had more mast cells than uninfected intestines, and these cells were often in close proximity to, and inside, the capillaries and lying close to fibroblasts of the muscularis layer and stratum granulosum. Intense degranulation of mast cells was encountered in all intestinal layers, especially near the E. truttae body.