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

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 (P<0.01) membrane shape change at 20, 30, 60, 120, and 300 sec after Cf stimulation. A maximum of 85.8±3.2% of newborn PMNs exhibited such C-finduced shape changes by 120 sec, which was significantly greater (P<0.01) than the maximum stimulation (67.7±4.3%) attained with adult PMNs. These data indicate enhanced kinetics of induced newborn PMN membrane shape change in response to Cf stimulation. We also compared stimulus-specific superoxide anion (O ₂ ^– ) 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,P<0.05) than did adult PMNs (12.4±0.3 nmol O ₂ ^– )/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 <0.05) than did adult PMN (5.5 ±0.5 nmol O ₂ ^– /10⁶ PMN). These findings collectively document biochemical and morphological differences between newborn and adult PMNs as determined by stimulusspecific O ₂ ^– generation and C_f-induced membrane shape change. Such differences may be important to neonatal disease susceptibility.