Blood group A immunodeterminants on human red cells differ in biologic activity and sensitivity to alpha-N-acetylgalactosaminidase.
BACKGROUND
Epitopes of blood group A antigen can be enzymatically cleaved from red cells (RBCs), but the extent of cleavage required for normal survival in allogeneic blood transfusion recipients is unknown. Therefore, the cleavage rates were studied for A antigen epitope binding of 1) complement-activating anti-A, 2) Dolichos biflorus anti-A, lectin, and 3) hemagglutinating anti-A during incubation with a purified alpha-N-acetylgalactosaminidase, E.C. 3.2.1.49 (alpha-GalNAc'ase).


METHODS
Suspensions of group A RBCs were incubated with alpha-GalNAc'ase. Cells were removed at intervals, washed, and tested for loss of binding by monoclonal, polyclonal, and complement-activating anti-A, D. biflorus anti-A1 lectin, and Ulex europaeus anti-H lectin.


RESULTS
A epitopes binding D. biflorus lectin were highly susceptible to alpha-GalNAc'ase; simultaneously with their loss, binding with U. europaeus lectin emerged. Loss of complement-mediated hemolysis was slower. A epitopes binding hemagglutinating anti-A were most resistant. Cleavage of A epitopes from membrane glycosphingolipids with short oligosaccharide chains was similarly resistant. Rates of cleavage from A1 and A2 RBCs were similar.


CONCLUSIONS
RBC epitopes of blood group A differ in susceptibility to cleavage and biologic reactivity, which suggests that subsets mediating important biologic functions exist on functionally and topographically distinct membrane glycoconjugates.
Hoskins
L C
LC
Department of Medicine, Veterans Affairs Medical Center, Cleveland, Ohio, USA.
Larson
G
G
Naff
G B
GB
D000017:ABO Blood-Group System / Q000276:immunology*; D000911:Antibodies, Monoclonal; D001665:Binding Sites; D000939:Epitopes / Q000378:metabolism*; D004912:Erythrocytes / Q000276:immunology*; D005434:Flow Cytometry; D006028:Glycosphingolipids / Q000097:blood; D006384:Hemagglutination; D006596:Hexosaminidases / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D037102:Lectins / Q000378:metabolism; D009844:Oligosaccharides / Q000097:blood; D037121:Plant Lectins; D048809:alpha-N-Acetylgalactosaminidase
D000017:ABO Blood-Group System; D000911:Antibodies, Monoclonal; D000939:Epitopes; D006028:Glycosphingolipids; D037102:Lectins; D009844:Oligosaccharides; D037121:Plant Lectins; C036850:Ulex europaeus lectins; C036554:dolichos biflorus agglutinin; D006596:Hexosaminidases; C482722:NAGA protein, human; D048809:alpha-N-Acetylgalactosaminidase