Common evolutionary origin of the immune and neuroendocrine systems: from morphological and functional evidence to in silico approaches

Ten years ago, we surmised that there was a common evolutionary origin for the immune and neuroendocrine systems. This was based on morphological and functional results indicating that a common pool of molecules is shared by the two systems, both in invertebrates and vertebrates. In the past decade, numerous molecular biology experiments have confirmed sequence similarity between invertebrate and vertebrate neuroimmune mediators, such as corticotrophin-releasing hormone. However, sequence similarity-based approaches were inadequate for analyzing other immune-related molecules, such as helical cytokines. This review covers older, and more recent findings on invertebrate immune- and neuroendocrine-related molecules with an evolutionary perspective, and suggests that protein-folding recognition algorithms are a fundamental tool in understanding the evolution of immune- and neuroendocrine-related molecules.