[Immune defenses of newborn infants].

Host defenses to bacterial infection are deficient in the neonate. This deficiency contributes to severe systemic infections in newborns. Phagocytosis of bacteria is decreased due to deficient activity of phagocytic cells and opsonines. Immunoglobulin secretion depending on B and helper T cell activities is strongly depressed due to immaturity of both populations. Therefore, maternal immunoglobulins of IgG type which cross placenta since 32 weeks of gestation play an important role in newborn defenses to bacteria even if this protection is incomplete.