Abstract

Chile is one of the main producers of Atlantic salmon (Salmo salar) in the world, with a currently marine culture biomass close to 350,000 tons. This biomass suffers mortalities close to 3,500 tons per month, being the infectious diseases the second primary cause of this problem (19.6%). The major agent of this mortality is the bacteria Piscirickettsia salmonis (67.9% of cases). P. salmonis is an intracellular facultative pathogen that generates systemic infections evading the immune response of the host by infection of macro- phages and avoiding the respiratory burst. To control this pathogen, Chilean aquaculture has used antibiotics, immunostimulants and vaccines. However, no strategy has given optimal results. In this context, more data of immunological parameters in field conditions are necessary for a more accurate characterization of the real state of the fish when is facing a P. salmonis infection. In this work, we have focused on quantifying molecular markers associated with the process of antigen presentation, which is crucial to achieve coordination between innate and adaptive immune response. For this, we evaluated the gene expression of interferon gamma (ifng), transforming growth factor beta (tgfb) and interleukins (il-10, il-12 and il-15); markers of cell lineage (cd83 and cd80/86); major histocompatibility com- plex I and II (mhci and mhcii); T cell receptor alpha (tcra); immunoglobulin M (igm); and annexin1 (anxa1) by qPCR from spleen of S. salar at two sea farm centers (Puelche and Punta Islotes). Puelche reported two outbreaks of P. salmonis, while Punta Islotes didn’t report any fish infected with the pathogen during the sampling time. Gene expression results showed that fish from Puelche increased the gene expression of ifng, tgfb, cd83, cd80/86, mhcii, il-10, il-12, igm and anxa1 at different sampling points. On the other hand, fish from Punta Islotes showed an increase of the gene expression of il- 10 and cd80/86, mhcii and il-12. Finally, the correlation of data showed a proportional detection between markers of the same sea farm center and inversely proportional between centers with P. salmonis (Puelche) and without P. salmonis (Punta Islotes).