Research on the ontogeny of immunity includes investigations on comparative developmental immunobiology, developmental immunogenetics, genetic defects of immunity, primary immunodeficiencies, early thymic development, and teratogens and nutritional deficiencies that affect development of the immune system. Emphasis is on the temporal development and function of immune cells, complement factors, and cytokines in the developing embryo, fetus, infant, and child. The program supports studies to: diagnose congenital infections; characterize and understand the sequential development of host defense mechanisms to congenital and pediatric infections; and study vertical transmission of pathogenic agents and evaluate their roles in teratogenesis and fetal wastage.