Developmental immunology of the newborn

Despite advances in antimicrobial therapy and neonatal intensive care, neonatal infections continue to be an important determinant of childhood morbidity and mortality in developed and third world countries. This article reviews the current understanding and updates of the developmental aspects of the neonate's specific host defense systems. The susceptibility of neonates to infection clearly is caused by their immune deficiency in the innate and specific immune host defense systems. The impaired neonatal T-cell functions are largely caused by the predominance of the CD45RA naive phenotype, efficiencies in cytokine production, and decreased CD40L expression on CD4+ T helper cells. These deficiencies lead to diminished T-B-cell collaboration, which causes lower immunoglobulin production and poor isotype switching. These deficiencies affect other immune effector cells, and lead to further compromises in other immune functions.