Impaired lymphocyte transformation with phytohemagglutinin The response of lymphocytes to PHA is measured by their ability to transform and to undergo mitosis. UMLS:C4025625 HP:0003347 Normal peripheral blood lymphocytes, when stimulated by phytohemagglutinin (PHA) are cytotoxic for homologous and heterologous cells but not for autologous cells in monolayer culture. The cytotoxic effect is thought to be indicative of the immunological competence of the lymphocytes. Abnormal lymphocyte physiology