Ab reacts with sialylated Lea-active pentasaccharide (sialylated lacto-N-fucopentose II). It recognizes the sialic acid-containing residue of the monosialoganglioside. Removal of the sialic acid residue with neuraminidase treatment eliminates positive reactivity with this antibody. Sialyl Lea is synthesized from type 1 blood group precursor chains and is present in individuals expressing the Lea and/or Leb blood group antigens.