Introduction - what is ontogenesis? 9 Ontogenesis of immunity of the human foetus 12 Development of the cellular substrate of the immune system . . . . . . 13 . Development of the lymphatic system . . . . . . . . . . . . . . 14 . . Synthesis of immunologically active proteins - the complement components and immunoglobulins - in the foetal period 18 Complement components . . . . . . . . . . . . . . . . . . 18 . Immunoglobulin synthesis . . . . . . . . . . . . . . . . . 23 . B lymphocytes with surface membrane immunoglobulins . . . . . . 26 Transmission of antibodies anrl immunoglobulins from mother to foetus 29 Transplacental transmission of specific antibodies . . . . . . - . 29 Transplacental transmission of immunoglobulins . . . . . . . . . 33 Physiological conditions for the transmission of immunoglobulins from mother to foetus . . . . . . . . . . . . . . . . . . . . . 36 . . . . Mechanism of transplacental transmission of IgG . . . . . . . . . 39 . Role of the Fe fragment of the IgG molecule and of cell receptors in the transplacental transmission of IgG . . . . . 42 Antibacterial mechanisms of the amniotic fluid . . . . . . . . . . 45 . . Ontogenesis of the foetus's cellular immunity . . . . . . . . . . . . 4 7 Incidence in the foetus of T lymphocytes forming spontaneous E rosettes 48 Functional activity of the T cell system . . . . . . . . . . . . . 49 . . Response offoetallymphocytes to phytohaemagglutinin (PHA) stimulation in vitro . . . . . . . . . . . . . . . . . . . . . . . 49' . . . . . Proliferative response of foetal lymphocytes to stimulation by allogenic cells in mixed lymphocyte cultures . . . . . . . . . . . . . . 51 . . Effector activity of foetal lymphocytes - cytotoxicity . . . . . . . . 52 Chronological survey of the commencement of foetal immunocompetence 53 Immunity of the physiological neonate Natural (nonspecific) neonatal immunity . . . . . . . . . . . . . 61 . .