Lectins are a group of proteins that bind specifically to monosaccharides, disaccharides, and oligosaccharides and are characterized by the ability to agglutinate cells, polymerized oligosaccharides or precipitate polysaccharides and glycoproteins (1).  The agglutination and precipitation reactions are based on the multivalency of the majority of lectins; there are monovalent lectins which will not support agglutination, polymerization, or  precipitation (2-4).  Ricin from castor bean was the first lectin identified in 1888 by Hermann Stillmark but there was no substantial interest in the proteins until much later (5).  Lectins are found in a variety of organisms including plants (6) and fungi (7).  There a variety of animal lectins characterized by specificity, tissue localization, and function (8,9). Galactins bind to β-D-galactoside and are associated with inflammation(10).  C-lectins, so named because they require the presence of calcium ions for binding, include endocytic lectins which are membrane proteins which bind and participate in the endocytosis of certain glycoproteins (11,12), collectins which are characterized by the presence of collagenous domain (13) and are pattern recognition molecules (14), and selectins which mediate the interaction of leukocytes with endothelial cells (15)  Mannose binding lectins which are classified as collectins initiate the lectin complement activation pathway(16,17).   Mannose-binding lectin (MBL) as pattern recognition molecule binds to repetitive microbial surface patterns resulting in the activation of the MAST (MBL-associated serine protease) pathway which in turn can activate either the classical pathway or alternate pathway.

1. Sharon, N. and Lis, H., Lectins, 2nd edn., Introduction, Chapter 1, pps. 1-4, Kluwer Academic, Dordrecht, Netherlands, 2003.
2. Thomasson, D.L. and Doyle, R.J., Monovalent concanavalin A, Biochem.Biophys.Res.Commun. 67, 1545-1552, 1975.
3.  Tanaka, I., Abe, Y., Hamada, T., Yonemitsu, O., and Ishii, S., Monovalent monomer derivative of concanavalin A produced by photochemically induced alkylation, J.Biochem. 89, 1643-1646, 1981.
4.  Shahzad-ul-Hussan, S., Gustchina, E., Ghirlando, R., Clore, G.M., and Bewley, C.A., Solution structure of the monovalent lectin microvirin in complex with Manα(1-2)Man provides a basis for anti-HIV activity with low toxicity, J.Biol.Chem. 286, 20788-20796, 2011.
5. Sharon, N. and Lis, H., Lectins, 2nd edn., History, Chapter 2, pps. 5-32, Kluwer Academic, Dordrecht, Netherlands, 2003.
6.  Puztai, A., Plant Lectins, Cambridge University Press, Cambridge,United Kingdom, 1991; Plant Glycobiology: A  Sweet Role of Lectins, Glycoproteins, Glycolipids, and Glycans, ed. C.A. Albenne, E.J.M. van Damme, E.I. Janet, and N.I. Lannoo, Fronteirs Media, S.A., Lausanne, Switzerland, 2015.
7. (Varrot, A., Basheer, S.M., and Imberty, A., Fungal lectins: structure, function and potential applications, Curr.Opin.Struct.Biol. 23, 678-685, 2013.
8.  Lectins Biomedical Perspectives, ed. A. Duszta and S.Bardocz, Taylor & Francis, London, United Kingdom, 1995.
9.  Animal Lectins A Functional View, ed. G.R.Vaste and H. Ahmed, CRC Press, Boca Raton, Florida, USA, 2007.
10. Sundblad, V. Morosi, L.G., Geffner, J.R., and Rabinovich, G.A., Galactin-1: A jack-of-all-trades in the resolution of acute and chronic inflammation, J.Immunol. 199, 3721-3736, 2017.
11.  McAbee, D.D., Jiang, X., and Walsh, K.B., Lactoferrin binding to the rat asialoglycoprotein receptor requires the receptor’s lectin properties, Biochem.J. 348, 113-117, 2000.
12.  Johannes, L., Wunder, C., and  Shafaq-Zadah, M., Glycolipids and lectins in endocytic uptake processes, J.Mol.Biol. 428, 4792-4818, 2016.
13. Howard, M., Farrar, C.A., and Sacks, S.H., Structural and functional diversity of collectins and ficolins and their relationship to disease, Semin.Immunopathol. 40, 75-85, 2018.
14.  Degn, S.E. and Thiel, S., Humoral pattern recognition and the complement system, Scand.J.Immunol. 78, 181-193, 2013.
15.  McEver,R.P., Selectins: initiators of leucocyte adhesion and signalling at the vascular wall, Cardiovasc.Res. 107, 331-339, 2015.
16. (Speth, C., Prodinger, .M. Würzner, R., Stoibert, H., and Dierich, M.P., Complement, in Fundamental Immunology, 6th edn., ed. W.E. Paul, Chapter 33, pps. 1047-1078, Lippincott, Williams & Wilkens/Wolters Kluwer, Philadelphia, Pennsylvania, USA, 2008.
17. Paréj, K., Dobó, J., Závodszkym, P., and Gál, P., The control of the complement lectin pathway activation revisited, Mol.Immunol. 54, 415-422, 2013.