Partial characterization of eosinophilic granule cells (EGCs) and identification of mast cells of the intestinal lamina propria in rainbow trout (Oncorhynchus mykiss). Biochemical and cytochemical study

Summary— The role of intestinal eosinophilic granule cells (EGCs) is still a subject of discussion. The aim of this study was to obtain additional functional data for a better characterization of these cells. Biochemical studies indicated the presence of small amounts of histamine, a characteristic and consistent marker of mast cells, in the posterior gut. On the other hand, histamine is always absent from homogenates of isolated EGCs. Using colorimetric assays, we were able to show aryl sulphatase B activity (18.5 ± 3.7 nM nitrocatechol/10⁶ cells) and detected peroxidase (1.86 ± 0.03 ng/10⁶ cells) in EGC homogenates. A cytochemical study enabled us to localize peroxidase in the granules of EGCs. These cells can also phagocytose latex beads. EGCs should thus be considered as homologous with mammalian eosinophils and not with mast cells. The screening for cells in the mucosae containing chondroitin sulphate revealed sparsely represented cells in the loose connective tissue in immediate proximity to blood capillaries. These cells could be mucosal mast cells.