Development or the newborn immune system.

The newborn immune system differs quantitatively and functionally from adul ts. At birth, the immune system is partially immature, resulting in deficie ncy in cell-mediated cytolysis, immunoglobulin synthesis and cytokine produ ction. The most clearly defined deficit in neonatal phagocytosis defenses i s diminished neurophil storage. T cell function is diminished, including T cell-mediated cytotoxicity and T cell help, for B cell differentiation. Sel ective decreases in cytokine production by T cells may contribute to all of these deficits. One of the fundamental differences between adults and newb orns for T cell functions resides in whether or not the patient had prior e xposure to antigens. Significant immune responses to antigens can be obtain ed in the neonatal period. These response are qualitatively different from those induced in adults with a predominance of TH2 pattern. (C) 1999 Elsevi er Paris.