Increased production of superoxide anion by neonatal polymorphonuclear leukocytes stimulated with a chemotactic peptide

In order to assess the functional property of neonatal polymorphonuclear leukocytes (PMNs), we studied their chemoattractant-stimulated superoxide anion (O2-) production using a soluble chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) as a PMN stimulus. O2- production by neonatal PMNs was increased: when stimulated with 10(-7)M FMLP, O2- values (nanomoles; mean +/- SE) produced by 10(6) PMNs were 16.5 +/- 1.3 for neonatal PMNs and 12.6 +/- 0.6 for adult PMNs (p less than .02). When studied under various concentrations (10(-9) to 10(-6)M) of FMLP, neonatal PMNs produced more O2- than adult cells under the stimulation of a lower concentration (10(-8)M) as well as a higher concentration (10(-7)M) of FMLP. The increased O2- production by neonatal PMNs was also observed under their stimulation by phorbol myristate acetate. Neonatal and adult PMNs produced equal amounts of O2- when stimulated with a particulate stimulus of opsonized zymosan. To analyze further the mechanism for the increase in FMLP-induced O2- production by neonatal PMNs, we next studied whether there was some abnormality in their FMLP receptors. Neonatal PMNs had normal numbers of FMLP receptors; the receptor numbers (mean) per cell were 54,000 in neonatal PMNs and 56,000 in adult cells. Additionally, the FMLP receptors had normal affinity for the peptide. These results demonstrate that the increased production of O2- by FMLP-stimulated neonatal PMNs is not due to the abnormality of its binding to the receptors but is due to that of the subsequent events.