Neonatal neutrophil inflammatory responses: Parallel studies of light scattering, cell polarization, chemotaxis, superoxide release, and bactericidal activity

Neutrophil dysfunction among newborn infants, especially those born prematurely, is well recognized, but the mechanism responsible for this phenomenon is yet to be clarified. In this study, we evaluated the stimulus response coupling in neutrophils from 90 healthy newborns and 96 healthy adults in an effort to establish whether defective neonatal neutrophil function is a result of impaired signal perception or immature responsiveness. Measurement of rapid- and slow-light scattering responses (LSR) to 1 μM FMLP stimulation revealed that neonatal neutrophils have about one-half the corresponding responsiveness of adult cells (rapid-LSR: 6.1 ± 3.1 arbitrary light intensity units vs. 12.0 ± 2.8, P<.001; and slow-LSR: 5.0 ± 2.5 vs. 9.1 ± 2.0; P<.001). The same markedly reduced activity was observed in newborn neutrophil chemotaxis and bactericidal activity in comparison with adult cells. Nevertheless, low FMLP concentrations (less than 1 nM) induced no difference in cell polarization between newborn and adult neutrophils, yet at higher FMLP concentrations, the newborn revealed significantly reduced cell polarization. Our data suggest that newborn infants bear a fully functional FMLP signal perception but lack the full capacity of inflammatory responsiveness.