A species-specific determinant on β2-microglobulin required for Ly49A recognition of its MHC class I ligand

Abstract

The mouse inhibitory NK cell receptor Ly49A recognizes the mouse MHC class I molecule H-2Dk. The present study focuses on the species specificity of β2-microglobulin (β2m), an invariant component of MHC class I, in the interaction between Ly49A and H-2Dk. Transfection of the β2m-defective mouse cell line R1E/TL8x.1 with human (h) β2m induced cell-surface expression of H-2Dk, but failed to protect the cells from killing by Ly49A+ NK cells. In contrast, the cells transfected with mouse (m) β2m were protected from killing by Ly49A+ NK cells. These data indicate that Ly49A distinguishes mβ2m from hβ2m when it recognizes the H-2Dk complexes. To identify the species-specific determinant of β2m required for Ly49A recognition of H-2Dk, we prepared a panel of mβ2m mutants and tested the H-2Dk that included each of the β2m mutants for its capacity to engage Ly49A on NK cells. Ly49A failed to functionally recognize the H-2Dk that included the mβ2m with K3R and Q29G mutations. Moreover, Ly49A was able to recognize the H-2Dk that included the hβ2m with R3K and G29Q mutations. These data indicate that Lys3 and Gln29 consist of the central part of the species-specific determinant of β2m required for Ly49A recognition of H-2Dk. The two residues are conserved in the mouse and the rat, in which NK cells use Ly49 family molecules as the receptors specific for MHC class I. These results suggest functional importance of β2m in NK cell recognition of target cells.