Epitope mapping of Ly-49G and G-like receptors: CK-1 antibody defines a polymorphic site of functional interaction with class I ligand.

Ly-49 receptors regulate mouse natural killer cell functions. Members of the polymorphic Ly-49 multigene family recognize specific alleles of major histocompatibility complex class I (MHC I) or MHC I-like proteins. Previous studies have provided insight into the nature of Ly-49A and -C interaction with their high-affinity MHC I ligands, H-2Dd and Kb, respectively. Unlike Ly-49C, recognition of MHC I by Ly-49A is regulated in part by residues within the beta4-beta5 loop of its ectodomain. Ly-49A and -G are within the same Ly-49 subfamily, and both receptors recognize Dd. However, there have been no studies that define specific sites on Ly-49G that mediate class I MHC recognition. The Ly-49G receptors of different inbred mouse strains can differ as a result of amino acid polymorphisms within their ectodomains. In this report, we have generated a novel antibody, CK-1, which recognizes Ly-49G(B6) and a Ly-49G(B6)-like receptor, Ly-49M(nonobese diabetic), but not Ly-49G(BALB/c). By exploiting the differences within ectodomains of C57BL/6 and BALB/c Ly-49G allele products, we identified epitopes recognized by the Ly-49G-specific antibodies CK-1 and Cwy-3, whose epitopes mapped within the beta4-beta5 loop and the beta1 strand, respectively, and were nonoverlapping. Although both antibodies specifically recognized the Ly-49G(B6) ectodomain, Cwy-3 was unable to block its interaction with MHC I, and CK-1 significantly inhibited it. The importance of residues within the beta4-beta5 loop in Ly-49G recognition demonstrates that its interaction with MHC I is similar to that of Ly-49A but not Ly-49C.