A antigen

A Antigen

A major blood group (ABO) antigen which defines human blood type A, and assumes the codominant allele at the ABO locus is either blood group A or H.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

A antigen

A major blood group–ABO antigen that defines the blood type A, which assumes the codominant allele at the ABO locus is either blood group A or H. Cf B antigen, Bombay phenotype, H antigen.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.