, Volume 25, Issue 5, pp 323-328

A transposable epitope of HLA-137, B40 molecules

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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 α2 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.