Molecular characterization and expression analysis of interleukin 15 (IL15) and interleukin-15 receptor subunit alpha (IL15Rα) in dojo loach (Misgurnus anguillicaudatus): Their salient roles during bacterial, parasitic and fungal infection

Interleukin 15 (IL15) is a pleiotropic cytokine that participates in innate and adaptive immunity along with its receptor α-chain (IL15Rα). In order to investigate the potential roles of IL15 and IL15Rα in dojo loach (Misgurnus anguillicaudatus), we firstly cloned the cDNA sequence of Ma-IL15 and Ma-IL15Rα, which contain 1096bp and 1236bp and code proteins of 193 amino acids and 210 amino acids, respectively. A short signal peptide and Pfam IL15 domain were found in Ma-IL15, while a highly conserved sushi domain existed in Ma-IL15Rα. Ontogeny analysis indicated that significantly increased expression of Ma-IL15 and Ma- IL15Rα mRNA were detected in larvae from 1d to 7d post hatching, while relative high expression levels were detected in both systematic and mucosal immune-related tissues of adult dojo loach. Then three dojo loach infection models with F. columnare G4, I. multifiliis and Saprolegnia parasitica were constructed, which resulted in increased skin goblet cells and serious lesions in gill. Ma-IL15 and Ma-IL15Rα showed different expression patterns in different tissues during three infection models. Ma-IL15Rα mRNA was found to be more significantly elevated than Ma-IL15 after infection with F. columnare G4 in all examined tissues including kidney, spleen, gill and skin. I. multifiliis infection induced higher expression of Ma-IL15 in mucosal tissues including skin and gill, while it mainly increased Ma-IL15Rα expression in kidney. Moreover, our study firstly evaluated the influence of fungal infection on IL15 and IL15Rα expression in teleost, and it is interesting to find that both Ma-IL15 and Ma-IL15Rα expression showed consistent up-regulation after Saprolegnia parasitica infection compared to two other infection models. Therefore, our results suggest that Ma-IL15 and Ma-IL15Rα possess important defensive roles in systematic and mucosal tissues of dojo loach during bacterial, fungal and parasitic infection.