Bw4-reactive and Bw6-reactive antibodies recognize multiple distinct HLA structures that partially overlap in the alpha-1 helix.
Bw4 and BW6 epitopes are expressed by mutually exclusive sets of HLA-B alleles and some HLA-A and HLA-C alleles. To test whether antithetical structures are required to express Bw4 and Bw6 epitopes, we measured binding of Bw4-reactive and Bw6-reactive alloantibodies and mAbs to HLA-B7 variants. A triple substitution of HLA-B7 alpha-1 helix residues 80, 82, and 83 created Bw4 and destroyed Bw6 epitopes detected by alloantibodies and mAbs. Both Bw4-reactive and Bw6-reactive mAbs competed for binding to HLA-B7 variants with single substitutions at residues 82 and 83. Substitutions of residues H93 and D119 which form a salt bridge in HLA-A2 also permitted binding by both Bw4-reactive and Bw6-reactive mAbs, suggesting that Bw4 and Bw6 epitopes are conformationally dependent. Six Bw4-reactive mAbs showed four distinct patterns of binding to HLA-B7 variants. Detailed analysis of 74 HLA-B7 single-residue variants showed that Bw6-reactive SFR8-B6 binding was prohibited by mutations altering the distal end of the alpha-1 helix and the nearby connecting loop. In contrast, Bw6-reactive BB7.6 binding required both alpha-1 and alpha-2 helix residues. Thus, Bw4-reactive and Bw6-reactive Abs recognize multiple distinct HLA structures that partially overlap in the alpha-1 helix. As both Bw4 and Bw6 epitopes are expressed by some HLA-B7 variants, mutually exclusive expression of Bw4 and Bw6 epitopes in naturally occurring HLA class 1 molecules may reflect evolutionary pressure.
Lutz
C T
CT
Department of Pathology, University of Iowa, Iowa City 52242.
Smith
K D
KD
Greazel
N S
NS
Mace
B E
BE
Jensen
D A
DA
McCutcheon
J A
JA
Goeken
N E
NE
D000911:Antibodies, Monoclonal / Q000276:immunology; D000915:Antibody Affinity; D002460:Cell Line; D000939:Epitopes / Q000276:immunology*; D005434:Flow Cytometry; D006680:HLA Antigens / Q000276:immunology; D015235:HLA-B Antigens / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007518:Isoantibodies / Q000276:immunology; D016297:Mutagenesis, Site-Directed / Q000235:genetics
D000911:Antibodies, Monoclonal; D000939:Epitopes; D006680:HLA Antigens; D015235:HLA-B Antigens; D007518:Isoantibodies