Heterogeneity of functional responses in differentiated myeloid cell lines reveals EPRO cells as a valid model of murine neutrophil functional activation.

Mature neutrophils display multiple functional responses upon activation that include chemotaxis, adhesion to and transmigration across endothelial cells, phagocytosis, and pathogen destruction via potent microbicidal enzymes and reactive oxygen species. We are using myeloid cell line models to investigate the signaling pathways that govern neutrophil functional activation. To facilitate these studies, we have performed a direct comparison of functional responses of human and murine myeloid cell line models upon neutrophil differentiation. Our results show that EPRO cells, promyelocytes that undergo complete neutrophil maturation, demonstrate a full spectrum of functional responses, including respiratory burst, chemotaxis toward two murine chemokines, and phagocytosis. We also extend previous studies of granulocyte-colony stimulating factor-induced 32Dcl3 cells, showing they demonstrate chemotaxis and phogocytosis but completely lack a respiratory burst as a result of the absent expression of a critical oxidase subunit, gp91(phox). Induced human leukemic NB4 and HL-60 cells display a respiratory burst and phagocytosis but have defective chemotaxis to multiple chemoattractants. We also tested each cell line for the ability to up-regulate cell-surface membrane-activated complex-1 (Mac-1) expression upon activation, a response mediating neutrophil adhesion and a surrogate marker for degranulation. We show that EPRO cells, but not 32Dcl3 or NB4, significantly increase Mac-1 surface expression upon functional activation. Together, these data show that EPRO and MPRO cells demonstrate complete, functional activation upon neutrophil differentiation, suggesting these promyelocytic models accurately reflect the functional capacity of mature murine neutrophils.