Identification and characterization of CD152 in Nile tilapia (Oreochromis niloticus) playing roles in host immune response against bacterial pathogens

Abstract

The CD152, as named CTLA-4 (Cytotoxic T lymphocyte-associated antigen-4), is an important costimulatory molecule on the surface of T cells and plays an essential role in the cell-mediated immune response. In this work, Nile tilapia (Oreochromis niloticus) CD152 (OnCD152) was successfully cloned, and its characterization in response to bacterial pathogens and interaction with its ligand OnCD80/86 was also investigated. The open reading frame (ORF) of OnCD152 was 705 bp, encoding a polypeptide with 234 amino acids. The OnCD152 protein shared some homology with other known CD152 molecule from teleost species, containing conservative key sites, namely YPPPY, GNGT and four cysteine residues (Cys 45, Cys 97, Cys 123, Cys 151). The mRNA level of OnCD152 was extensively expressed in the collected healthy tissues. Following the stimulation of Poly (I:C), Streptococcus agalactiae and Aeromonas hydrophila, CD152 was significantly upregulated in the head kidney and spleen. The transcriptional upregulations of OnCD152 were also detected in Nile tilapia leukocytes after in vitro stimulations with Poly (I:C), S. agalactiae and A. hydrophila. In addition, the recombinant protein (r)OnCD152 was purified, and its binding ability to (r)CD80/86 strengthen with the increase of concentration. Taken together, this study demonstrated that OnCD152 was likely involved in host immune response against bacterial pathogens. Moreover, this research first cover about the capacity of OnCD152 binding with ligand CD80/86 in Nile tilapia (Oreochromis niloticus), which enrich the understanding for exploring the CD152 function in immune response in teleost fish in the future.