Chemotactic factor induced neutrophil shape changes in whole blood. A comparison of adults and neonates.

To define further the nature of the decreased responsiveness of neonatal neutrophils to chemotactic factor stimulation, neutrophil shape change induced by various concentrations of N-formyl-methionyl-leucyl-phenyl-alanine (fMLP) was studied using a whole blood assay. Samples from 48 full term neonates and paired healthy adult controls were examined. The neutrophil response to the chemotactic peptide was assessed by the morphologic transformation from a spherical to a bipolar shape in monolayer blood smears made from fresh whole blood samples. Neonatal neutrophils were found to have increased responsiveness relative to adult controls at low concentrations of fMLP (10(-11) to 10(-9) M), resulting in a significantly lower calculated chemotactic peptide concentration necessary for a 50 percent maximal response (ED50) in neonatal cells (1.01 X 10(-9) M compared to 2.25 X 10(-9) M). The maximal response at higher concentrations of fMLP (5.0 X 10(-9) to 10(-6) M) showed no differences between neonatal and adult cells, thereby supporting the concept that the early cellular events of the chemotactic factor activation in neonatal neutrophils are functionally intact.