Immunomodulation of the innate response in common carp Cyprinus carpio by ß-glucan feeding and pathogenic infection

Abstract

Two major components of the common carp Cyprinus carpio innate response, i.e. the C-reactive protein (CRP) and the complement system, have been analysed in common carp either orally immunostimulated with ß-glucan or infected with a pathogen or both. Immune response was examined at different levels, from serum circulating protein levels or activity to related gene expression in a wide range of immune related tissues such as liver, head kidney, mid-gut, gills and spleen. In addition, recombinant technologies were investigated in order to generate and produce subsequent amounts of carp CRP. Oral administration of ß-glucan significantly stimulated carp CRP and complement responses with elevated serum CRP levels and complement activity and up- and down regulation of related genes in immune related tissues from 7 days of treatment. A subsequent intraperitoneal injection of LPS or Poly(I:C) as mimicries of bacterial and virus infection respectively also did have significant effects on the production (gene expression) and the circulation (scrum levels or activities) of these acute phase proteins. In addition, results from a challenge conducted on common carp with Aeromonas salmonicida, the causative agent of furunculosis, have shown that ß-glucan enhanced and stimulated carp CRP and complement responses to the bacterial infection. These findings arc of importance in respect to the use of ß-glucan as an alternative low cost strategy to the use of vaccines or antibiotics to enhance and stimulate the fish immune system. Innate response was analysed in carp infected with the Koi Herpes Virus (KHV), the etiological agent of a virulent and lethal disease. Results have shown a serum CRP level 10 fold increase and a serum complement activity 5 fold increase in less than 72 hours, revealing that CRP and complement act as acute phase reactants in response to KHV infection in common carp.