Construction and functional test of a chicken MHC-I (BF2*15)/peptide tetramer

The major histocompatibility complex class I (MHC class I) peptide tetramer is a sensitive and valuable tool to evaluate antigen-specific cytotoxic T lymphocytes (CTLs) of many animal species. To date, no chicken MHC class I peptide tetramer has been reported. In this report, we describe construction and functional evaluation of a chicken MHC-I (BF2*15)/peptide tetramer. To construct the chicken MHC class I peptide tetramer, genes of the chicken MHC-I α chain (BF2*15) and β2 microglobulin (Chβ2m) were synthesized by RT-PCR from the total RNA of PBMCs and the signal sequences were deleted. The BF2*15 was then fused with the BirA substrate peptide (BSP) sequence at the C terminus. Next, the synthesized PCR products of BF2*15 and Chβ2m were cloned into the expression vector pET-28a (+) and expressed in Escherichia coli strain BL21 (DE3). Highly purified BF2*15-BSP heavy chain and Chβ2m were obtained by a Ni2+ NTA column affinity purification, yielding approximately 1.6 mg of BF2*15-BSP and 2.4 mg of Chβ2m per 1 g of the pelleted bacteria. The purified BF2*15-BSP heavy chain and Chβ2m were refolded with synthetic peptide originated from infectious bronchitis virus nucleoprotein (IBV N71–78) in refolding buffer to generate the monomer of BF2*15/peptide complex. The monomer was then biotinylated and tetramerized using PE-labeled streptavidin. Upon functional evaluation of the construct by using flowcytometry, we observed that 3.65% of CTLs were specific to IBV nucleoprotein. This demonstrates that the CTL response of IBV-infected chicks could effectively be evaluated using the prepared MHC-I BF2*15/peptide tetramer.