The CD55 (HI55a) antibody recognizes the human cell surface antigen CD55 (complement decay-accelerating factor, DAF), a GPI linked molecule widely e, Xenopus/Amphibian,pressed on human peripheral blood granulocyte,Mouse,onocyte, and some lymphocytes and erythrocytes. CD55 recognizes C4b and C3b fragments that condense with cell-surface hydro, Xenopus/Amphibian,yl or amino groups during their activation. This interaction interferes with the conversion of C2 and factor B to amplify the complement cascade. CD55 polymorphism is responsible for the Cromer blood group system.