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In this study, we investigated the influence of serotonin on the development and functioning of T- and B-cell-mediated immunity during ontogenesis using the pharmacological model of serotonin depletion in rat fetuses. It has been demonstrated that prenatal serotonin deficiency resulted in a decrease in thymus and spleen weights, changes in their cellular composition, and long-lasting disturbances in cell-mediated and humoral immunity in postnatal ontogenesis. The data obtained suggest that serotonin may be considered a morphogenic factor in development of the immune system.

Cross-regulatory effects of immune and neuroendocrine systems on their appearance and functioning occur during a whole life period. At different stages of ontogenesis, the functions of these systems are diverse. In perinatal ontogenesis hormones, neuropeptides and neurotransmitters control the processes of growth and differentiation of various embryo tissues, particularly lymphoid. In the postnatal period, their functions are mostly in homeostasis maintaining of the immune system in response to changes of the environment. Conversely, transmitters of the immune system, such as cytokines, whose synthesis is increased in inflammation, and thymic peptides, program the development of the neuroendocrine system of the embryo. The perinatal period is crucial for final appearance of these systems. Changes in one of the interacting systems, caused by negative environmental factors at this stage, usually provoke changes in other developing systems for a long period. Plasticity of physiological systems in perinatal development allows the organism to adapt to changed conditions. However, these changes can limit physiological functions in interacting systems and induce the appearance of various pathologies in postnatal life.

Different aspects of the reciprocal regulatory influence of systems producing the immune and gonadotropin-releasing hormone (GnRH) in pre- and postnatal ontogeny are discussed in this review. GnRH is a neurohormone synthesized by a small population of neurons located in the anterior hypothalamus, which regulates the secretion of gonadotropines in the anterior lobe of the pituitary gland and they finally regulate the synthesis of sex steroids. Particular attention is given to analysis of the data involving the role of thymus peptides and cytokines in GnRH-system regulation in the normal condition and in the case of inflammation development caused by endotoxines in adult animals. The main prospects of the studies involving the influence of proinflammatory cytokines on GnRH-neuron migration and differentiation in prenatal ontogenesis are also discussed.

The liver, thymus, spleen, lymph nodes, palatine and pharyngeal tonsils, appendix and Peyer's patch were studied by morphological and immune methods in more than 100 human embryos of 3 to 34 weeks of development. The order of some organs development in the immune system is established. Key periods in the development of the thymus (5-12 weeks) and 18 weeks when peripheral organs enter the immune system are specified. Inherited perinatal pathology in abnormal lymphocytic composition in the organ is illustrated by the appendix.

Protracted prenatal irradiation of animals at the preimplantation stage of embryogenesis is shown to produce disturbances in the development of regulation systems, with their consequences persisting up to sexually mature period of postnatal life. Unknown before, these effects of preimplantation irradiation give the experimental confirmation to the main statement of the previously proposed theoretical concept of the "systemic teratogenesis": the ultimate effect of prenatal irradiation is a distortion of the structure of postnatal neuroimmunoendocrine regulation in the direction of overdevelopment of its endocrine component with the following coadaptive underdevelopment of the nervous and immune components.

The lecture presents information on the development of the immune organs in human foetus (thymus, spleen, lymph nodes, tonsilla, appendix, Peyer's plaques and blood) on the basis of literature and author's own data. Phenotypic composition of T- and B-lymphocytes in each organ and in the blood are given in both foetus and adults. The information presented is valid for the understanding of congenital immunodeficiencies and immunological confrontation between the mother and the foetus. It is shown that the thymic hormones may be present in the cells of some other organs close to the thymus by their origin.

The ante- and postnatal development of the thymus gland and mesenteric lymph nodes of the rats receiving oleandomycin in the period of placentation and organogenesis (the 8th-14th days of embryogenesis) was studied by using anatomical, histological and electron microscopical methods. Oleandomycin produced inhibition of lymphopoiesis against the background of an increase of eosinophilic and neutrophilic granulocytes, reactive changes of the microcirculatory bed and ultrastructural lesions of the blood capillary wall.