PROTEIN-UPTAKE BY INTESTINAL MACROPHAGES AND EOSINOPHILIC GRANULOCYTES IN TROUT - AN IN-VIVO STUDY

A homologous protein, recombinant trout somatotropin (rtST) and its he terologous counterpart, native bovine somatotropin (bST), were adminis tered anally to juvenile rainbow trout (Oncorhynchus mykiss). Plasma l evels of rtST, determined by radioimmunoassay, peaked between 15 and 6 0 min and remained high until 2 h after administration. Immunogold lab elling was used to follow the routes of transfer of rtST and bST, and to observe potential interaction between the hormones and the cells co nstituting the first line of non-specific defence, ie the macrophages infiltrated between epithelial cells, or dispersed in the subepithelia l lamina propria, and eosinophilic granulocytes (EGCs) of the lamina p ropria, whose properties have been considered to be similar to mammali an mast cells. Macrophages were immunolabelled for the homologous and heterologous proteins. EGCs took up the heterologous but not the homol ogous protein. This finding was confirmed using indirect immunofluores cence assay. EGCs could internalize foreign proteins transferred from the intestinal lumen to the lamina propria.