Phaseolus vulgaris agglutinin is the name ascribed to a family of lectins, each of which consists of four subunits. There are two different types of subunits. One appears to be involved primarily in red cell agglutination and has been designated the “E” subunit (for erythroagglutinin). The other type is involved in lymphocyte agglutination and mitogenic activity and has been termed the “L” subunit (for leucoagglutinin). These subunits combine to produce five isolectins.
PHA-L, with four “L” type subunits, does not agglutinate red cells but is a potent mitogen. PHA-L has been found to be an excellent, specific marker for use in anterograde neuronal tracing.