Neuroimmune chemical messengers and their conservation during evolution

Abstract

Cellular communication is mediated primarily by chemical signal molecules. This suggests that during the course of evolution, organisms in which this form of communication developed have greatly increased their chances of survival, ensuring that this trait passes on to their descendents. Interestingly, for the most part, these signaling molecules and their apparent systems/mechanisms have remained relatively intact during evolution. However, this principle of conservation does not preclude events that may lead to an old signal system being used in a new functional capacity. A classical example of this phenomenon can be observed in the immune and neuroendocrine systems. They share a common pool of identical molecules, i.e., opioids, involved in the maintenance of homeostasis, which occurs in both invertebrates and vertebrates. Specifically, many of these protein molecules, active as chemical messengers, are also derived from larger polypeptide gene products and classified into three families: the proopiomelanocortin (POMC), the proenkephalin and the prodynorphin families. In marine mussels the immunocytes produce and react to opioid peptides, demonstrating autocrine and paracrine signaling. Under stressful stimuli immune system alteration occurs, in part mediated by opioid signals, coupling these processes and demonstrating neuroimmune-regulatory phenomena. Additionally, both immune and nervous systems contain mammalian-cytokine-like molecules, which also interact with the endogenous opioid system. Recent data have demonstrated the presence of novel opiate receptors on human multi-lineage progenitor cells. Interestingly, these same receptors are found on molluscan neural cells, suggesting their early evolutionary origins and conservation. The only data on molluscan stem cells are the presence of CD14- and CD-34-like molecules on prohemocyte membranes. These data suggest that the highly sophisticated mammalian immune and neuroendocrine systems had their origins in their invertebrate counterparts. © 2009 Springer Netherlands.