Lepeophtheirus salmonis secretory/excretory products and their effects on Atlantic salmon immune gene regulation

Abstract

We have previously shown that Lepeophtheirus salmonis produces trypsin and prostaglandin E2 (PGE2) that are most likely responsible for the limited inflammatory response of Atlantic salmon to infection. After removal of the dopamine and PGE2, the immunomodulatory activity of unfractionated and pools of the fractionated secretions was determined by examining the effects of the secretions on Atlantic salmon immune gene expression. Incubation of macrophage-enriched isolates of Atlantic salmon head kidney cells with the unfractionated secretion + PGE2 revealed a significant inhibition of interleukin-1β (IL-1β) and major histocompatibility class I gene expression. Inhibition of lipopolysaccharide- induced IL-1β expression in the Atlantic salmon head kidney cell line (SHK-1) was observed when three pools of the secretory/excretory products were tested. Further purification of products within these pools revealed that fraction 1-2 could account fully for the inhibition of IL-1β expression in SHK-1 cells observed in pooled fraction 1. This study demonstrates that there are other immunomodulatory compounds produced by L. salmonis, in addition to PGE2 and trypsin, that can inhibit the expression of Atlantic salmon immune-related genes in vitro. © 2007 National Research Council.