Martin et al. BMC Genomics 2010, 11:418 http://www.biomedcentral.com/1471-2164/11/418 R E S E A R C H A R T I C L E Open Access Starvation alters the liver transcriptome of the innate immune response in Atlantic salmon (Salmo salar) Samuel AM Martin*, Alex Douglas, Dominic F Houlihan, Christopher J Secombes Abstract Background: The immune response is an energy demanding process, which has effects in many physiological pathways in the body including protein and lipid metabolism. During an inflammatory response the liver is required to produce high levels of acute phase response proteins that attempt to neutralise an invading pathogen. Although this has been extensively studied in both mammals and fish, little is known about how high and low energy reserves modulate the response to an infection in fish which are ectothermic vertebrates. Food withdrawal in fish causes a decrease in metabolic rate so as to preserve protein and lipid energy reserves, which occurs naturally during the life cycle of many salmonids. Here we investigated how the feeding or fasting of Atlantic salmon affected the transcriptional response in the liver to an acute bacterial infection. Results: Total liver RNA was extracted from four different groups of salmon. Two groups were fed or starved for 28 days. One of each of the fed or starved groups was then exposed to an acute bacterial infection. Twenty four hours later (day 29) the livers were isolated from all fish for RNA extraction. The transcriptional changes were examined by micro array analysis using a 17 K Atlantic salmon cDNA microarray. The expression profiling results showed major changes in gene transcription in each of the groups. Enrichment for particular biological pathways was examined by analysis of gene ontology. Those fish that were starved decreased immune gene transcription and reduced production of plasma protein genes, and upon infection there was a further decrease in genes encoding plasma proteins but a large increase in acute phase response proteins. The latter was greater in magnitude than in the fish that had been fed prior to infection. The expression of several genes that were found altered during microarray analysis was confirmed by real time PCR. Conclusions: We demonstrate that both starvation and infection have profound effects on transcription in the liver of salmon. There was a significant effect on the transcriptional response to infection depending on the prior feeding regime of the fish. It is likely that the energy demands on protein synthesis for acute phase response proteins are relatively high in the starved fish which have reduced energy reserves. This has implications for dietary control of fish if an immune response is anticipated. Background The immune response is a coordinated reaction mounted by a host in an attempt to control or destroy an invading pathogen. There are a multitude of different processes that occur during this response which are dependent on the type of pathogen, the route of infec- tion or the previous exposure to the pathogen. The * Correspondence: sam.martin@abdn.ac.uk Scottish Fish Immunology Research Centre, Institute of Biological and Environmental Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ, UK innate immune response includes both cellular and humoral elements. These can detect and neutralise pathogens [1] but manage to avoid attacking the hosts own tissues. Once an inflammatory immune response is initiated proinflammatory cytokines including IL-1b, IL-6, tumour necrosis factor a and a panel of chemokines instigate the coordinated expression of downstream genes. Fish have an increasingly well characterised innate immune system [2] with many genes being identified as having a role in controlling the immune response [3]. Transcriptome analysis has been performed in salmonid © 2010 Martin et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.