Major histocompatibility complex class IIα and II β of pufferfish ( Takifugu obscurus ): Identification and functional characterization in response to bacterial challenge

Abstract

Classical major histocompatibility complex (MHC) class II molecules play an essential role in immune system. In this study, MHC II α (Pf‐MHC II α ) and MHC II β (Pf‐MHC II β ) homology genes from pufferfish ( Takifugu obscurus ) were cloned and their functional characterization in response to bacterial challenge was identified. The nucleotide sequences of the open reading frames (ORFs) of pufferfish Pf‐MHC IIα and Pf‐MHC IIβ were 708 bp and 750 bp, encoding 235 aa and 249 aa, respectively. The structure of Pf‐MHC II α or Pf‐MHC II β contained a signal peptide, an α 1/ β 1 domain, an α 2/ β 2 domain, a transmembrane region and a cytoplasmic region. Multiple sequence alignment and phylogenetic analysis showed that Pf‐MHC II α and Pf‐MHC II β molecules had the highest similarity with Fugu rubripes ( Takifugu rubripes ). Cellular localization analysis indicated that the distribution of Pf‐MHC II α and Pf‐MHC II β was in the lymphocyte membrane and cytoplasm. qRT‐PCR results showed that Pf‐MHC IIα and Pf‐MHC IIβ expressed relatively high in skin, gills and gut. In addition, after stimulation challenge in vitro (lipopolysaccharide, or polyinosinic: polycytidylic acid) and in vivo ( A. hydrophila ), the mRNA expressions of Pf‐MHC IIα and Pf‐MHC IIβ were significantly up‐regulated in lymphocytes and in tissues of skin, gills, gut and head kidney. Moreover, Pf‐MHC II α or Pf‐MHC II β neutralization reduced the ability of A. hydrophila to induce the expressions of lymphocyte cytokines ( TNF‐α , IL‐1β and IL‐10 ). Overall, it is speculated that Pf‐MHC II α and Pf‐MHC II β may play an important role in the host response against A. hydrophila in pufferfish.

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