Narcissus pseudonarcissus lectin or agglutinin (NPL/NPA) is isolated from wild daffodils. This lectin is composed of four subunits and has a molecular weight of 59 kDa. It agglutinates rabbit erythrocytes but is non-reactive with human erythrocytes. NPA has an isoelectric point between pH 4.2 and pH 4.6 with a specific binding activity toward alpha-D-mannose, although studies have suggested that the purified lectin may have greater affinity for internal mannosyl residues than for nonreducing terminal units. 

Human studies have found NPA to be nearly non-mitogenic, but it has been reported through an in vitro study that mitogenicity of NPA is age-related, with lymphoproliferative response of peripheral blood mononuclear cells (PBMC) in umbilical cord blood has a sevenfold increase than adult blood. NPA has also been found to be mitogenic for PBMC from lambs and not adult sheep.