Phytohemagglutinin (PHA)

Phytohemagglutinin (**PHA**) is a family of closely related plant lectins found predominantly in red kidney beans (*Phaseolus vulgaris*) and other legumes. It consists mainly of two types of subunits—leukocyte-reactive (L) and erythrocyte-reactive (E)—which combine into tetrameric isolectins with varying biological activities. PHA-L preferentially agglutinates leukocytes and acts as a potent T-cell mitogen by stimulating lymphocyte proliferation; PHA-E primarily aglutinates erythrocytes. The protein binds complex oligosaccharides containing galactose, N-acetyl-glucosamine, and mannose residues on the surface glycoproteins of mammalian cells. In laboratory settings, phytohemaglutinnin serves as an important tool for inducing T-cell division in immunology studies or triggering apoptosis via upregulation of proapoptotic proteins like Bax. When ingested from inadequately cooked beans it can be highly toxic due to its ability to disrupt cellular processes through strong binding interactions with gut epithelial cells[1][2][4][5].

Other names

PHAPhytohaemagglutinin (alternative spelling)Leucoagglutinin (PHA-L)Erythroagglutinin (PHA-E)Mitogenic phytohemagglutininRed kidney bean lectin

Binds specific carbohydrate structures on cell surfaces leading to agglutination and mitogenic stimulation[2][4].