Mistletoe, Viscum album, is a species of parasitic plant, which has no roots but attaches itself to a host tree from which it absorbs the sap through one or more suckers. It is a sub-shrub of the Santalaceae family.

Viscum album (ML I / VAA) lectin, is a Galactose-specific lectin. It is a dimer with a molecular weight of 115 kDa. ML-I is both a type II ribosome inactivating protein and a chitin-binding lectin. This lectin has additionally been shown to inhibit B cell hybridomas and P815, EL-4, Ke37, MOLT-4, and Up37 tumor cell lines by apoptosis induction.

VAA is not blood group specific, but has an affinity for terminal β-D-galactosyl residues. VAA inhibits protein synthesis similarly to Ricin (RCA60) and inhibits allergen induced histamine release in vitro from human leukocytes.