Major histocompatibility complex class IIA and IIB genes of loach (Misgurnus anguillicaudatus): Molecular cloning and expression analysis in response to bacterial and parasitic challenge

Abstract

The major histocompatibility complex (MHC) is a crucial component of the immune response in vertebrates including teleost fish, which is responsible for the presentation of foreign antigens. In this study, we firstly cloned and identified the gene sequences of MHC IIA and MHC IIB from dojo loach (Misgurnus anguillicaudatus). The full-length cDNA of Ma-MHC IIA and Ma-MHC IIB contained an open reading frame (ORF) of 708 and 756 bp encoded a predicted protein of 235 and 251 amino acids, respectively. The structure of Ma-MHC IIA and Ma-MHC IIB consists of a signal peptide, an α1/β1 domain, an α2/β2 domain, a transmembrane region and a cytoplasmic region, which are similar with other fish species. The deduced amino acid sequence of Ma-MHC IIA and Ma-MHC IIB molecules shared high similarity with those of other teleost fish, especially with Cyprinidae, by multiple sequence alignment and phylogenetic analysis. Quantitative real-time PCR (qRT-PCR) in different tissues showed that the Ma-MHC IIA and Ma-MHC IIB mRNA expressed relatively higher in mucosal tissues such as skin, gill and intestine than other tissues. Importantly, it was the first time that two infection models of the loach with bacteria (Flavobacterium cloumnare G4) and parasite (Ichthyophthirius multifiliis) were constructed to study the function of Ma-MHC II genes in immune response. And the significant up-regulated expression of Ma-MHC II genes were not only detected in spleen and kidney, but also in mucosal tissues including skin and gill. Our results indicated that Ma-MHC II genes might play an essential role in the skin and gill mucosal immune response to help loaches defense the pathogenic bacteria and parasite.