Phytohemagglutinin-P (PHA-P) is a lectin obtained from the kidney bean (Phaseolus vulgaris). It comprises two subunits, leucoagglutinin (PHA-L) and erythroagglutinin (PHA-E), each forming a tetramer held together through non-covalent interactions.
PHA-P represents the mucoprotein form of the molecule. It is used to promote cell proliferation in lymphocyte cultures. Given its strong red blood cell agglutinating activity, it was historically used to isolate leukocytes from whole blood.