News WP3

In workpackage 3, led by Professor Øystein Evensen at the Norwegian School of Veterinary Science, work has been carried out to characterize the inflammatory and early immune responses of resistant and susceptible families of Atlantic salmon.

Differences in susceptibilities to sea lice infection between different species of salmon have been indicated since the early 1990s. A recently performed large scale challenge trial including a high number families challenged with L. salmonis revealed differences in susceptibility between families. We are currently analyzing samples obtained from this trial to understand why some families are better at resisting infection. The task is challenging as large variation in the number of lice is observed among individuals, both within and between families.

When parasitic copepods attach to a host, the immune defense system is expected to be activated in order to combat the infection. This includes activation of a variety of immune cells and induction of numerous immune responses at the site of infection, but also in internal organs. Our preliminary profiling of gene expression in skin and spleen is indicative of L. salmonis releasing immunomodulatory substances that skew the inflammatory and early immune response in salmon, where genetic components also seem to play a role. Judging by a number of genes with roles inflammation and early immunity, susceptible fish defer immunomodulation imposed by sea lice to a lesser extent than resistant fish.  Studies also include assessment of skin responses by morphological methods with the aim to evaluate how cells residing in the epithelium, including mucus cells, keratinocytes and infiltrating immune cells respond to attached lice.

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