MHC class II alpha, beta and MHC class II-associated invariant chains from Chinese sturgeon (Acipenser sinensis) and their response to immune stimulation

The major histocompatibility complex class II (MHC II) molecules play a vital role in adaptive immune response through presenting antigenic peptides to CD4⁺ T lymphocytes. To accomplish this physiologic function, the MHC class II-associated invariant chain interacts with the MHC II α/β subunits and promotes their correct assembly and efficient traffic. Here, we isolated the cDNAs of MHC II α, β and MHC II-associated invariant chains (designated as CsMHC II α, CsMHC II β, and CsMHC II γ) from Chinese sturgeon (Acipenser sinensis). The CsMHC II α, β, and γ mRNAs were widely expressed in Chinese sturgeon, and the highest expression was found in spleen for CsMHC II α and β chains, while in head kidney for CsMHC II γ chain. Stimulation to Chinese sturgeon with inactivated trivalent bacterial vaccine or polyinosinic polycytidylic acid (poly(I:C)) up-regulated the expressions of CsMHC II α, and β mRNAs, and their transcripts were overall more quickly up-regulated by poly(I:C) than by bacterial vaccine. Poly(I:C) induced higher CsMHC II γ expression than bacterial vaccine in intestine and spleen, while lower than bacterial vaccine in head kidney and liver. When co-expressed in mouse dendritic cells, the CsMHC II γ chain bound to both the MHC II α and β chains. Furthermore, the over-expressed CsMHC II γ chain, not CsMHC II α or CsMHC II β chain, activated NF-κB and STAT3 in mouse dendritic cells, and induced TNF-α and IL-6 expressions as well. This activity was nearly abolished by mutation of the Ser29/Ser34 to Ala29/Ala34 in CsMHC II γ. These results suggested that CsMHC II α, β, and γ chains might play important role in immune response to pathogen microbial infection of Chinese sturgeon possibly via a conserved functional mechanism throughout vertebrate evolution, which might contribute to our understanding the immune biology of sturgeons.