Agaricus bisporus agglutinin / lectin (ABA / ABL) is a mixture of two phytohemagglutinins with similar specificities for carbohydrate receptors (PHA-A and PHA-B). Both PHA-A and PHA-B are heterogeneous by SDS-PAGE. The mushroom PHA will have a molecular weight of 58.5 kDa as determined by gel filtration that corresponds to tetramer. Each monomer has 2 distinct carbohydrate binding sites, one for galactose-β-1,3-N-acetylgalactosamine (also called Thomsen-Friedenreich antigen or T disaccharide) and another for galactose-β-1,3-N-acetylglucosamine.

ABA has a non-specific blood group since PHA-A and PHA-B agglutinate erythrocytes independent of their blood group type. Agaricus bisporus has an anti-proliferative effect on cancerous cells. ABA can be internalized by clathrin-coated vesicles after binding to surface glycoproteins.