Grass carp (Ctenopharyngodon idellus) invariant chain of the MHC class II chaperone protein associates with the class I molecule

The invariant chain (Ii) is an important immune molecule, as it assists major histocompatibility complex (MHC) class II molecules to present antigenic peptides. The relationship between the Ii and MHC molecules in teleosts remains poorly understood. This study focused on the molecular structure of grass carp Ii (gli), its organ distribution, correlations with gene transcription, and the association with MHC. gli cDNA was cloned using designed degenerate primers and the rapid amplification of cDNA ends method (RACE). The gli sequence was 92%-96% similar to that of other teleosts, but only 52%-67% similar to that of mammals, respectively. The gli gene was distributed in all 12 organs examined by PCR. The gli gene transcription levels were markedly higher in organs enriched with immune cells than in other organs (P < 0.01). Moreover, positive correlations were detected between transcription levels of the gli and gMhcl or II genes in different organs (r = 8.415-8.523, P = 0.001). The gli co-localized on endomembrane systems with either class I or II molecules in co-transfected cells observed by a laser confocal. Further testing confirmed that the gli bound gMHCI and II molecules. Taken together, these results indicate that the gli is associated with MHC class I and II molecules, suggesting homology of both MHC molecules. (C) 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).