Immunologic deficiencies in small-for-dates neonates.

Health is dependent upon good nutrition because of the interactions of immunologic function with nutritional status. Full-term neonates--and even more so prematures--present with various immaturities of their humoral and cellular immunologic mechanisms, particularly during the first days of life. Foetal growth retardation causes further deficiencies to the immature neonatal host defence mechanisms by decreasing thymic hormone activity and by reducing the numbers and activity of T and B-lymphocytes in their peripheral blood. Furthermore, very low levels of IgG 1 immunoglobulin and reduced bacteriocidal capacity of polymorphonuclear neutrophils have been found in small-for-dates neonates. Impaired immunocompetence in growth-retarded neonates is probably the main cause of the increased frequency and severity of infections they develop.