Immunomodulatory effect of cathelicidins in response to a β-glucan in intestinal epithelial cells from rainbow trout

The aim of the present study was to characterize intestinal immune mechanisms involved in the response to β-glucans in rainbow trout. Among the immune effectors regulated in response to immunostimulants, host defense peptides (HDPs) are abundantly expressed in epithelial linings, suggesting their important role in the mucosal immune response. Therefore, the immunomodulatory properties of expressed HDPs in the epithelial intestinal cells of rainbow trout in response to the β-glucan, zymosan, were assessed. The results showed that zymosan increased the production of the HDP, cathelicidin, and the cytokine, IL-1β, in the intestinal epithelial RTgutGC cell line at the transcript and protein levels. Thus, cathelicidin-2 variants were produced and were shown to (i) induce the production of IL-1β in RTgutGC cells and (ii) display a synergic effect with zymosan in IL-1β upregulation. Importantly, the colocalization of both rtCATH-2 and IL-1β was detected in the intestinal epithelial cells of rainbow trout fed with a 0.3% zymosan-supplemented diet. We propose that trout cathelicidins are expressed by intestinal epithelial cells and exert immunomodulatory effects to improve the local intestinal immune response triggered by immunostimulants.