RESUMO
Nucleotide binding and oligomerization domain (NOD)1 and NOD2 are important cytoplasmic pattern recognition receptors (PRRs) and key members of the NOD-like receptor (NLR) family. They sense a wide range of bacteria or their products and play a key role in inducing innate immunity. This report describes the role of NOD1 and NOD2 receptors signalling in innate immunity in the Indian major carp, mrigal (Cirrhinus mrigala). Tissue-specific expression analysis of NOD1 and NOD2 genes by quantitative real-time PCR (qRT-PCR) revealed their wide distribution in various organs/tissues. In the untreated fish, the highest expression of NOD1 and NOD2 was detected in liver and blood, respectively. Stimulation with NOD1- and NOD2-specific ligands, i.e. iE-DAP and MDP, activated NOD1 and NOD2 receptor signalling in vivo and in vitro resulting in significant (p<0.05) induction of downstream signalling molecule RICK, and the effector molecules IL-1β, IL-8 and IFN-γ in the treated group as compared to their controls. In response to both Gram-positive and Gram-negative bacterial infections, NOD1 and NOD2 receptors signalling were activated and IL-1β, IL-8 and IFN-γ were induced. These findings highlight the important role of NOD receptors in eliciting innate immune response during the pathogenic invasion to the fish.