Les interactions immuno-neuroendocriniennes et leurs implications cliniques

The interactions between the immune and neuroendocrine systems and their clinical implications

Division d'Endocrinologie, Diabétologie et Métabolisme, Centre Hospitalier Universitaire Vaudois – CHUV, CH-1011 Lausanne, Suisse

Résumé

Les systèmes immunitaire et endocrinien sont reliés par un réseau d’interactions bidirectionnelles qui, d’une part, permettent aux hormones de moduler les fonctions immunologiques et, d’autre part, permettent au système immunitaire de produire des effets neuroendocriniens. Ainsi, des hormones tels les glucocorticoïdes, la corticolibérine (CRH), l’hormone de croissance, la prolactine et la somatostatine, sont des modulateurs de réponses immunitaires et inflammatoires, alors que les cytokines modulent la fonction des axes corticotrope, gonadotrope, thyréotrope et somatotrope. Ces interactions immuno-neuroendocriniennes sont donc impliquées dans de nombreuses situations physiologiques et physiopathologiques. Elles jouent ainsi un rôle dans l'hypogonadisme, l’hypothyroïdie et l’arrêt de croissance qui surviennent lors de maladies infectieuses ou inflammatoires. Quant aux interactions avec l’axe hypothalamo-hypo- physo-surrénalien, elles permettent de contrôler la réponse inflammatoire afin d’éviter qu'une exagération de cette réponse ne mette en danger l’intégrité de l’organisme.

Abstract

The endocrine and immune systems are interrelated via a bidirectional network in which hormones affect immune function and, in turn, immune responses are reflected in neuroendocrine changes. This bidirectional communication is possible because both systems share a common « chemical language » that results from a sharing of common ligands (hormones and cytokines) and their specific receptors. Cytokines are important partners in this crosstalk. They play a role in modulating the hypothalamo-pituitary-adrenal (HPA) axis responses at all three levels : the hypothalamus, the pituitary gland and the adrenals. Acute effects of cytokines are produced at the central nervous system level, particularly the hypothalamus, whereas pituitary and adrenal actions are slower and are probably involved during prolonged exposure to cytokines such as during chronic inflammation or infection. Several mechanisms have been proposed by which peripheral cytokines may gain access to the brain. They include an active transport through the blood-brain barrier, a passage at the circumventri- cular organ level, as well as a neuronal pathway through the vagal nerve. The immune-neuroendocrine interactions are involved in numerous physiological and pathophysiological conditions and the interactions with the HPA axis may represent a mechanism through which the immune system, by stimulating the production of glucocorticoids, avoids an overshoot of inflammatory response. They may also be involved in the state of hypogonadism, of hypothyroidism and growth inhibition which can occur during inflammatory and infectious diseases. The crosstalk between the immune and endocrine systems is important to homeostasis, since the interactions can produce various appropriate adaptative responses when homeostasis is threatened.