A lectin is “a protein or glycoprotein of non-immune origin, not an enzyme, that binds to carbohydrates and agglutinates cells”(1). Lectins are naturally occurring substances, most commonly derived from plant or sometimes invertebrate sources, that can be exploited in the laboratory to detect and reveal carbohydrate structures in or on the surface of cells in very much the same way that antibodies can be used to reveal specific antigens. Lectins can detect very subtle alterations in cellular glycosylation. This is of interest in metastasis research as there is increasing evidence that marked glycosylation changes can attend both transformation to malignancy and tumor progression. Lectins are named after the source from which they are derived-sometimes the Latin binomial (e.g.,Bandeirea simplicifolialectin orDolichos bifloruslectin), sometimes the common name (e.g., peanut lectin or wheatgerm lectin), or some-times by a slightly obscure historical term (e.g., Concanavalin A [Con A] for the lectin fromCanavalia ensiformis, the jack bean). The term lectin is used fairly interchangeably with the older term “agglutinin,” as in peanut agglutinin orHelixpomatiaagglutinin. Lectins are often referred to by an abbreviation for their names, for example, PNA (peanut agglutinin) or DBA (Dolichos biflorusagglutinin); obscurely, PHA, which actually stands for phytohaemagglutinin is, for historical reasons, the abbreviation usually employed for the lectin derived fromPhaseolusvulgaris. Many sources yield more than one lectin, termed isolectins, which may have quite different carbohydrate binding specificities (e.g., the gorseUlexeuropaeusyields two major isolectins,Ulex europaeusagglutinin I [UEA-I], which has a strong binding preference for fucose, andUlex europaeusagglutinin II [UEA-II], which has a strong binding preference forN-acetylglucosamine).
