The evolution of echinoderm immunology

Echinoderms are deuterostome, and occupy the top taxonomie position of invertebrates, where is the evolutionary linkage between invertebrates and vertebrates. This is a critical phylogenetic vantage point to infer both the early evolution of bilaterian immunity and the underpinnings of the vertebrate adaptive immune system. The available published literatures on echinoderm immunological mechanisms are compiled and discussed here to understand its evolution process and the hot spots or directions in future investigations. Echinoderms have an innate immune system like vertebrates but their adaptive attributes have not been observed. Its immune responses are based on coelomocytes activity working in parallel with a variety of humoral factors that react directly with invading pathogens. Comparative studies of immune functions in echinoderms have demonstrated that there is a complement system in echinoderms that appears to have alternative pathway and lectin pathway but lack classical pathway and terminal pathway. The sea urchin innate immune system has a number of large gene families. Further investigations are needed to understand the unknown immune-associated genes, proteins, immune signaling pathways and effector molecules, and to know the origin, the underlying mechanisms and evolution of innate immune system.