ACTH and its role in immune-neuroendocrine functions. A comparative study.

Adrenocorticotropic hormone (ACTH) belongs to the melanocortine group of related peptides which share a common precursor, the pro-opiomelanocortin (POMC). Melanocortin expresses its functional effects by the stimulation of specific G-protein coupled receptors. To date, five receptor subtypes have been cloned. The POMC gene has been highly conserved during evolution, and ACTH has been found in different cells from invertebrates to vertebrates to vertebrates, including man. With regards the immune system, the presence of melanocortin receptors and the production of ACTH have been reported in invertebrate and vertebrate immuno-competent cells. Among its various physiological effects, ATCH has been shown to play a central role in immmune responses, such as chemotaxis and phagocytosis, in lower and higher forms of life. Moreover, ACTH is a key actor in stress response, and the complex cascade of events observed in vertebrates is reproduced and concentrated in intvertebrate immunocytes. On the basis of the present findings, ACTH should be considered an important immuno-regulator, forming part of the complex mosaic of relationships between the immune and neuroendocrine system which appears to have been substantially maintained over the course of evolution.