SOME ASPECTS OF THE HUMORAL IMMUNITY AND THE PHAGOCYTIC FUNCTION IN NEWBORN-INFANTS

Newborn infants, particularly those born prematurely, are prone to dev elop life-threatening pyogenic infections. Different studies have demo nstrated impairment of various aspects of the humoral immunity and the phagocytic activity of neutrophils in newborns. We conducted a compre hensive study evaluating the complement function (CH50 and AP50) and t he level of the vast majority of the complement components (Clq, Clr, Cls, C2-C9, FB and properdin) in preterm and full-term newborn infants as compared to adults. Furthermore, we investigated the effect of aut ologous and heterologous serum on the bactericidal activity of neutrop hils, by crossing newborn serum with adult cells and vice versa. Resul ts showed that preterm and full-term newborns have an impaired complem ent activity as compared to adults (CH50 P<0.05, AP50<0.01) and signif icantly reduced complement components except for C7, which was found t o be normal in full-term infants and in most appropriate-for-gestation al age preterm newborns at 34-36 weeks. A statistically significant co rrelation was found between gestational age and the level of most of t he complement components. CH50 and AP50 also showed a positive trend w hich, however, was not statistically significant. No correlation was f ound between birthweight and complement activity or complement compone nt levels. The neutrophil bactericidal activity of full-term newborns was about one-third that of adults (P<0.001). Adult serum improved the bactericidal activity of newborn neutrophils by 93%, indicating a con siderable neonatal humoral defect. Conversely, neonatal serum blunted the adult bactericidal activity by 86%. Our results support the fact t hat both humoral and phagocytic functions in newborn infants are impai red, which may possibly account for their increased tendency to develo p severe pyogenic infections.