Alterations in complement-induced shape change and stimulus-specific superoxide anion generation by neonatal calf neutrophils

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Abstract
Increased susceptibility of neonates to infection may be related to defects in newborn neutrophil (PMN) functional activities, including altered responses to complement fragments (Cf) and defective microbicidal activity. We therefore compared the kinetics of newborn and adult bovine PMN membrane shape change responses following stimulation with zymosan-activated plasma (ZAP) as a source of Cf. Measurement of PMN membrane shape change was a rapid, sensitive, and reproducible measure of Cf stimulation within a population of PMNs; a maximum of 67–85% of the PMNs exhibited easily detectable membrane ruffling, lamellipodia formation, and polarity within 2 min. Newborn PMNs exhibited significantly increased (PP2 − ) generation as a measure of respiratory burst activity after incubation of new-born and adult PMNs with soluble (phorbol myristate acetate, PMA) and particulate (opsonized zymosan, OZ) stimuli. When PMA was used as the stimulus, newborn PMNs generated significantly less O 2 − (9.3±0.5 nmol O 2 − /106 PMN,P2 − )/106 PMN). This finding was reversed when OZ was used as the stimulus; newborn PMNs generated significantly more O 2 − (7.7±0.4 nmol O 2 − /106 PMN,P 2 − /106 PMN). These findings collectively document biochemical and morphological differences between newborn and adult PMNs as determined by stimulusspecific O 2 − generation and Cf-induced membrane shape change. Such differences may be important to neonatal disease susceptibility.