Crustacean immunity

Abstract

Crustaceans have efficient means to defend themselves against most potential pathogens. Their hemocytes are crucial in these immune reactions and are capable of phagocytosis, encapsulation, nodule formation, and mediation of cytotoxicity. Recent progress in the in vitro handling of hemocytes, and the isolation and purification of several of the factors involved in the defense reactions show that the prophenoloxidase activating system (the proPO-system) and associated factors are important mediators of crustacean immunity. The use of purified factors of the proPO-system and separated hemocytes have made it possible to demonstrate in freshwater crayfish two proteins that are directly involved in cellular communication between different hemocytes. One of this proteins, a β-1,3-glucan binding protein present in the plasma, also appears to function as a recognition protein in the arthropod immune system. Another protein, a 76 kD protein derived from the granules of the hemocytes, is multifunctional and mediates hemocyte degranulation, spreading, and attachment. Also the prophenoloxidase itself and the prophenoloxidase activating enzyme, a serine proteinase, have recently been purified. Thus, it is now possible to elucidate the molecular details of the crustacean immune reactions in much more detail.