Abstract
The acute phase response (APR) is an early innate immune function that is initiated by inflammatory signals, leading to the release of acute phase proteins to the bloodstream to re-establish homeostasis following microbial infection. In this study we analysed the Atlantic salmon (Salmo salar) whole-genome database and identified five C-reactive protein (CRP)/serum amyloid P component (SAP) like molecules namely CRP/SAP-1a, CRP/SAP-1b, CRP/SAP-1c, CRP/SAP-2 and CRP/SAP-3. These CRP/SAP genes formed two distinct sub-families, a universal group (group I) present in all vertebrates and a fish/amphibian specific group (group II). Salmon CRP/SAP-1a, CRP/SAP-1b and CRP/SAP-1c and CRP/SAP-2 belong to the group I family whilst salmon CRP/SAP-3 is a member of group II. Gene expression analysis showed that the salmon CRP/SAP-1a as well as serum amyloid A-5 (SAA-5), one of the major acute phase proteins, were significantly up-regulated by recombinant cytokines (rIL-1β and rIFNγ) in primary head kidney cells whilst the other four CRP/SAPs remained refractory. Furthermore, SAA-5 was produced as the main acute phase protein (APP) in Atlantic salmon challenged with Aeromonas salmonicida (aroA(-) strain) whilst salmon CRP/SAPs remained unaltered. Overall, these data illustrate the potential different functions of expanded salmon CRP/SAPs to their mammalian homologues.
Highlights
The acute phase response (APR), a core part of the innate immune system, comprises a series of physiological and biochemical reactions including change of body temperature, vascular permeability, electrolyte levels, bone marrow-derived cells and acute phase proteins (APPs) production, which aims to re-establish homeostasis during an inflammatory response [5,15]
A single copy of serum amyloid A (SAA) gene has been characterised in several teleost species, such as Atlantic salmon (Salmo salar) [17], rainbow trout (Oncorhynchus mykiss) [36,48], Arctic char (Salvelinus alpinus) [15] and goldfish (Carassius auratus) [19] and its expression has been consistently shown to be increased in response to bacterial pathogens or bacterial related pathogen associated molecular patterns (PAMPs), confirming that fish SAA is a major APP
A number of studies have reported the presence of C-reactive protein (CRP)- and serum amyloid P (SAP)-like proteins in teleost fish which were named based on the binding properties compared with their mammalian homologues [3,11,33]
Summary
The acute phase response (APR), a core part of the innate immune system, comprises a series of physiological and biochemical reactions including change of body temperature, vascular permeability, electrolyte levels, bone marrow-derived cells and acute phase proteins (APPs) production, which aims to re-establish homeostasis during an inflammatory response [5,15]. The SAA genes have been identified in the human and mouse genome, with 4 and 5 copies sequenced in each species [15]. A single copy of SAA gene has been characterised in several teleost species, such as Atlantic salmon (Salmo salar) [17], rainbow trout (Oncorhynchus mykiss) [36,48], Arctic char (Salvelinus alpinus) [15] and goldfish (Carassius auratus) [19] and its expression has been consistently shown to be increased in response to bacterial pathogens or bacterial related pathogen associated molecular patterns (PAMPs), confirming that fish SAA is a major APP. Pentraxin-like proteins are ubiquitously present in all fish species examined to date and have been named according to the binding specificities comparable to the known mammalian CRP/. We analysed the expression profiles of salmon CRP/SAP-like molecules and SAA-5 in primary head kidney cells treated with cytokines and in liver of bacterial infected fish
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