Hypothalamic mechanisms of immunity

The present article considers a synthetical analysis of the results reported by our laboratory in the last twenty years in the field of neuroimmunomodulation. The studies we discuss here continue a previous research activity, a synthesis of which has also been published in this journal (Baciu, 1988). In that paper, we reported data concerning the role of the hypothalamic tubero-mammillary area in triggering of the phagocytic and of the secondary immune specific response. Here, we present an analysis of experimental facts gathered after 1988, and also of some prior to that date, which were not included in the above-mentioned review. They regard localizations, attained with stereotactical methods, of hypothalamic areas involved in maintenance of basal phagocytosis and of its circadian rhythm, of the phagocytic and of the primary and secondary specific response. We attempted to re-analyze these data in an integrative view, and accomplish a coherent image of the hypothalamic mechanisms of the nonspecific and specific immune response. The conclusion we draw is that the nervous system may exert its modulatory action upon the immune response in several ways: i) subsequent to a direct hypothalamic stimulation (electrical or through bacteria or bacterial products) or to a cortico-hypothalamic stimulation; ii) depending on the nature, intensity, duration, and frequency of the appropriate stimulus, it may either enhance the immune response, via neural and humoral pathways, or depress it; iii) via the hypothalamus-pituitary-adrenal axis. Nervous triggering and enhancement of the immune response are essential, their occurrence in the initial stages ensuring its favorable course. The finding that repeated electroconvulsant shocks, employed for hypothalamus stimulation in dogs of different breed, age, weight, and individual history, are followed by extremely variable changes of the phagocytic activity raises the question on the individuality of the immune response.