Newborn infants are more susceptible to
bacterial infections than adults. This susceptibility has been attributed to defects in humoral and cellular activity. Host cellular activity can be modified by factors produced by bacteria or the host in response to
infection. We assessed the effect of two factors associated with
gram-negative bacterial infection,
lipopolysaccharide (LPS) and
TNF-alpha, on polymorphonuclear neutrophilic granulocytes (PMN) obtained from adult or newborns (umbilical cord blood). PMN were primed in vitro with LPS (10 micrograms/L) or
TNF-alpha (10(-9) M) for 45 min and then assessed, using a chemiluminescence (CL) assay as an
indicator of oxidative radical production with formyl-
methionyl-leucyl-phenylalanine as the trigger for CL initiation. CL activity of unprimed PMN was similar for adults and newborns (13.3 and 13.7 CL units, respectively). After priming with LPS, CL activity was increased to 43.4 CL units for PMN from adults but to only 17.6 CL units for PMN from newborns (p < 0.001, adults versus newborn increment). Priming of PMN with LPS was most effective when autologous plasma was present. Using
FITC-conjugated LPS and a flow cytometry assay, we could demonstrate no difference between the binding affinity of LPS for adult and newborn PMN. However, formyl-
methionyl-leucyl-phenylalanine binding studies indicated that adult PMN had a higher number of binding sites.
TNF-alpha priming of newborn PMN was also ineffective. Adult PMN increased CL activity by 3.9-fold when primed with
TNF-alpha, whereas newborn PMN increased by only 1.75-fold (p < 0.005). This priming deficiency was not attributable to
TNF-alpha receptors because
phycoerythrin-conjugated
TNF-alpha was associated with PMN from adults and newborns equally. Thus, PMN from newborns are not primed effectively in vitro with LPS or
TNF-alpha. This defect may contribute to neonatal susceptibility to
bacterial infection.