Uptake of yeast cells in the Atlantic salmon (Salmo salar L.) intestine

• Anally intubated yeast were engulfed by large mononuclear cells in the intestinal lumen of salmon.
• Yeast were found in the epithelium, close to large nuclei of macrophage-like cells.
• Macrophage-like cells are possibly responsible for luminal neutralization and transepithelial transport.

The intestinal mucosa is an important port of entry for many pathogens. Information of antigen uptake mechanisms is essential to understand and to possibly prevent infections. In teleosts, several studies have aimed at investigating particulate uptake in the gastrointestinal system that seems to vary dependent on fish species and antigen. In the present study, particulate uptake in the Atlantic salmon intestine by anal intubation of yeast cells has been investigated. In the anal intubated fish, yeast were found in the epithelium close to nuclei of macrophage-like cells and inside large mononuclear cells in the intestinal lumen, indicating uptake and possible transport of large antigen particles over the epithelium by macrophage-like cells.