The Prophenoloxidase Activating System: The Biochemistry of Its Activation and Role in Arthropod Cellular Immunity, with Special Reference to Crustaceans

Abstract

Although modern immunology owes its origin largely to the pioneering work of Metchnikoff [40] and his observations of phagocytosis in the water flea, Daphnia, the study of “immune” processes in invertebrates has always lagged behind that of mammals. Indeed, it is only recently that plausible theories for the discrimination of self from non-self in invertebrates have been put forward and that fundamental techniques such as the separation of the various blood cell populations have been devised. As it is, there is still debate between invertebrate immunologists as to the true biochemical/molecular basis for non-self recognition in different invertebrate phyla, and foremost amongst the mechanisms proposed to account for recognition phenomena in the arthropods are the lectins, cell surface charge and, more recently, the prophenoloxidase activating system. To help clarify the picture for arthropods, the present review aims to re-evaluate some of the earlier work conducted on arthropod cellular immunity which gave rise to these concepts, and to reinterpret the data provided by the respective authors in the light of our present understanding of the prophenoloxidase activating system in crustaceans.