Aspects of the Atlantic salmon immune response during infection with the salmon louse, Lepeophtheirus salmonis (Krøyer, 1837)

Atlantic salmon (Salmo salar) were experimentally infected with Lepeophtheirus salmonis \ncopepodids and aspects of the host’s immune response investigated. Copepodid \nsecretory/excretory product (SEP) produced during early settlement was analysed using \nfast-protein liquid chromatography (FPLC), sodium dodecyl sulphate (SDS)- \nelectrophoresis and zymography. Following establishment and the appearance of the \nchalimus stages, the expression of the chemokine interleukin-8 (IL-8) in the heart, spleen, \nhead kidney, fins, liver and pyloric cæca was investigated using real-time (quantitative) \nPCR (qPCR). Furthermore, the secretions of L. salmonis chalimus were analysed for the \npresence of the prostanoid PGE2 using commercially available enzyme-linked \nimmunoassay (EIA) kits. \n \nAnalysis of copepodid secretory/excretory product suggested that any immunosuppressive \ncomponent is not proteinaceous in nature. Whilst there was a definite increase in protein \nconcentration of SEP relative to control SEP, further analysis using subtractive \nchromatographic analysis did not reveal any unique fraction present in either SEP or CSEP \nthat was absent in the other. Interleukin-8 expression levels in tissues changed following \nL. salmonis infection, with heart and spleen showing significant increases in IL-8 gene \nexpression, whilst the head kidney, fins, liver and pyloric cæca showed no significant \nincrease. The increase in splenic IL-8 expression may be linked to its role as one of the \nmajor secondary lymphoid organs. However, this is the first record of increase in IL-8 \nexpression in cardiac tissue. The secretions of L. salmonis chalimus were found to contain \nquantifiable levels of PGE2, albeit in highly variable quantities. This concurs with already \npublished findings for adult L. salmonis (see Fast, et al. 2004). It is proposed that the \nchalimus states us the PGE2 to modulate the hosts’ immune response at the site of \nattachment and feeding.