The invariant chain (Ii) is a molecular chaperone for major histocompatibility complex class II (MHC II) and is therefore intimately involved in the process of antigen presentation. However, it also acts as a receptor for various molecules including macrophage migration inhibitory factor. To determine the localization of Ii in the digestive system of the Muscovy duck (Cairina moschata) (MDIi), frozen tissue sections were prepared and immunofluorescence performed using a mouse anti-MDIi antibody. The results show that MDIi was highly expressed by a large number of suspected macrophages and dendritic cells in connective tissues of the mucosa lamina propria in the digestive tract. In comparison, MDIi was only weakly expressed, but polarly distributed, in epithelial cells of the mucosa and glands of the digestive tract. Hepatocytes and endothelial cells around the sinus of the liver also weakly expressed MDIi, while suspected dendritic cells and Kupffer cells strongly expressed it. The findings presented in this study provide initial data for future research on the function of Ii in different organs of the digestive tract of the Muscovy duck, especially in relation to mucosal immunity and the treatment of liver disease.

Key words: Digestive tract, Invariant chain, Muscovy duck (Cairina moschata), Tissue distribution