A transposable epitope of HLA-137, B40 molecules

Abstract

The monoclonal antibody M1340.2 defines a novel subtype of HLA-1340 that is expressed by the Sweig cell line. This molecule, called HLA-B40*, lacks an antigenic determinant that is common to HLA-137 and the HLA-Bw60 subtype of HLA-1340. Genes encoding HLA-B40* and HLA-BW60 have now been isolated and the amino acid sequences of these proteins compared with other HLA-13 locus molecules. These results show that HLA-B40* is a unique protein which differs from HLA-BW60 by eight amino acid substitutions. Comparison of the sequences for HLA-B40*, -Bw60, and -B7 localizes the MB40.2 epitope to a cluster of three substitutions at positions 177, 178, and 180 at the end of the 2 domain. Gene conversion or reciprocal recombination are postulated to have transferred this cluster of substitutions, and their associated epitope, during the evolution of HLA-B locus genes. The epitope may consist of an a helical segment which is exclusively found on MB40.2-positive molecules.