Complement activity and regulation in premature, late premature and term neonates

Abstract

Complement components (C3, C4, C5, C7, C9, factor B, C1inhibitor) are already synthesized early in fetal life although but present in early childhood with a relative deficiency in comparison with adult levels. Aim of this study was to evaluate a complement profile in premature (<34 weeks) and term babies focusing on the ontogeny of key regulatory proteins, which may allow an estimation of potential susceptibility to infection. Total complement activity (CH50, AP50), MBL, properdin, complement regulators (factors H, I and C1 Inhibitor) and C3a as marker of complement activation were assessed in three groups of healthy newborns in cord blood and at day 5 post partum: prematures from gestational age < 34 weeks (group 1), late premature from 34 to <37 weeks (group 2) and term neonates ≥37 weeks (group 3). Low, but age-related increasing CH50 values were observed in all three groups with lower titers in cord blood than in samples taken at day 5. Comparable low C3a levels excluded complement consumption as a consequence of activation. Plasma concentrations of C1 Inhibitor (protein and function) were below adult normal range only in preterm infants <34 weeks, but always lower in cord blood as compared those of 5th day. In contrast, factor I and the alternative pathway regulator, factor H, remained below normal adult range in all groups, even at day 5 pp. Levels of factor H and properdin increased with gestational age and no statistical significance among the 3 groups was detected for MBL levels. These results demonstrate the relative immaturity of the complement system and its regulators, especially in premature infants, predisposing to infections during the early neonatal period.