Functional differentiation of acute myeloid leukaemia blast cells

Little is known of the functional status of blast cells from patients with acute myeloid leukaemia (AML). We have studied phagocytosis and membrane receptors by flow cytometry (FCM), and secretory activities in blast cells from 24 AML patients prior to treatment. Blast cells from 11/16 patients attached N. meningitidis, and internalization occurred in 7/14. The phagocytosis of zymosan particles and N. meningitidis correlated linearly (r=0.9, p<0.01, n=11). Surface membrane expression of CD32 and CD11b was sufficient to account for opsonin-dependent attachment in all except one patient. A significant fraction of the blast cells attached, but did not internalize meningococci. CD32 and CD11b were non-functional in all the blasts from five patients, and in a subpopulation from seven additional patients. Significantly more large than small blasts expressed CD32, CD35 and CD11b (p<0.001). Phagocytosis was unrelated to the secretion of IL-1 alpha, IL-1 beta, and TNF alpha. In conclusion, AML blast cell function is related to receptor expression, cell size and granularity, and to FAB-type.