Modulation of genes related to the recruitment of immune cells in the digestive tract of trout experimentally infected with infectious pancreatic necrosis virus (IPNV) or orally vaccinated

• Several immune genes are regulated in the gut in response to IPNV or oral vaccination.
• IPNV induced the mobilization of IgM+, IgT+ and CD3+ cells to the digestive tract.
• Important immune differences were observed along the different gut segments.

There are still many details of how intestinal immunity is regulated that remain unsolved in teleost. Although leukocytes are present all along the digestive tract, most immunological studies have focused on the posterior segments and the importance of each gut segment in terms of immunity has barely been addressed. In the current work, we have studied the regulation of several immune genes along five segments of the rainbow trout (Oncorhynchus mykiss) digestive tract, comparing the effects observed in response to an infectious pancreatic necrosis virus (IPNV) infection to those elicited by oral vaccination with a plasmid coding for viral VP2. We have focused on the regulation of several mucosal chemokines, chemokine receptors, the major histocompatibility complex II (MHC-II) and tumor necrosis factor α (TNF-α). Furthermore, the recruitment of IgM+ cells and CD3+ cells was evaluated along the different segments in response to IPNV by immunohistochemical techniques. Our results provide evidences that there is a differential regulation of these immune genes in response to both stimuli along the gut segments. Along with this chemokine and chemokine receptor induction, IPNV provoked a mobilization of IgM+ and IgT+ cells to the foregut and pyloric caeca region, and CD3+ cells to the pyloric caeca and midgut/hindgut regions. Our results will contribute to a better understanding of how mucosal immunity is orchestrated in the different gut segments of teleost.