Complement factor 9 deficiency in serum of human neonates

Area of Science:

• Immunology
• Neonatal Immunology

Background:

• Neonates exhibit a less developed immune system compared to adults.
• The complement system, particularly the terminal pathway involving complement factor C9 (C9), plays a crucial role in innate immunity and bacterial clearance.

Purpose of the Study:

• To investigate the concentration and functional activity of C9 in neonatal sera.
• To assess the bactericidal capacity of neonatal sera against Escherichia coli.
• To determine the effect of supplemental C9 and IgG on neonatal serum bactericidal activity.

Main Methods:

• Quantification of C9 serum concentrations in mothers and neonates.
• Assessment of serum bactericidal activity against Escherichia coli O7w:K1:NM.
• Evaluation of the impact of exogenous C9 and IgG supplementation on bacterial killing and C9 deposition.

Main Results:

• Neonatal sera showed significantly lower C9 concentrations (less than 42 µg/ml) compared to maternal sera (260 ± 47 µg/ml).
• Neonatal sera demonstrated reduced bactericidal activity against E. coli, with only 3 of 14 samples significantly reducing bacterial survival.
• Supplementation with C9 enhanced the bactericidal capacity of neonatal sera, and supplemental IgG further potentiated C9 deposition and bacterial killing.

Conclusions:

• Neonatal sera possess diminished concentrations of C9, contributing to impaired bactericidal function against E. coli.
• Exogenous C9 can restore and enhance the bactericidal activity of neonatal sera.
• The combined presence of C9 and IgG is crucial for effective bacterial clearance in neonates, highlighting potential therapeutic targets.