Two class I genes of the chicken MHC have different functions: BF1 is recognized by NK cells while BF2 is recognized by CTLs

The function of the chicken’s major histocompatibility complex (MHC or B complex) class I major (BF2) and minor (BF1) glycoproteins is compared for their expression, ability to present viral antigens to cytotoxic T lymphocytes (CTLs), and interaction with natural killer (NK) cells. MHC-restricted CTLs recognized virus antigen in the context of the BF2*21 major glycoprotein but not the BF1*21 minor glycoprotein. Marek’s disease virus (MDV), a large DNA virus known to reduce the cell surface expression of class I glycoprotein, reduced the expression of BF2 glycoprotein while BF1glycoprotein expressions are remained as no change or slight increase. In addition, the expression of BF1*21 class I glycoprotein protected target cells from NK cell lysis while the expression of the BF2*21 class I glycoprotein enhanced NK cell lysis of target cells. Therefore, BF1 and BF2 provide two different cellular immune functions; BF1 negatively regulates the NK cell killing activity and BF2 restricts the antigen specific CTL immune response.