Lectins, of either plant or animal origin, are carbohydrate binding proteins that interact with glycoprotein and glycolipids on the surface of animal cells. The Galectins are lectins that recognize and interact with β-galactoside moieties. Galectin-1 is an animal lectin that has been shown to interact with CD3, CD4, and CD45. It induces apoptosis of activated T-cells and T-leukemia cell lines and inhibits the protein phosphatase activity of CD45. Recombinant human Galectin-1 is a 14.5 kDa protein containing 134 amino acid residues.