The role of complement and antibodies in the impaired bactericidal activity of neonatal sera against gram-negative bacteria.

The bactericidal action of serum is one of the mechanisms protecting higher organisms from infection by gram-negative bacteria. Complement (C) activation by the classical or alternative pathways plays a main role in this protective action. The bactericidal activity of normal newborn sera against some gram-negative bacteria is less efficient than that of normal adult sera. The reason for this may be connected with the damaged alternative and classical pathways of C activation and with the decreased levels of third -C3 and ninth -C9 factors of C system. A physiological deficiency of IgM antibodies may contribute also to the diminished bactericidal activity of newborn sera. Impaired activity of sera favours the susceptibility of neonates to bactericidal infection.