Cell adhesion molecules and antioxidative enzymes in a crustacean, possible role in immunity

Abstract

The question as to how the immune defence of an invertebrate animal is initiated and coordinated has largely been unanswered. This short review focuses on recent discoveries about crayfish hemolymph proteins, which may play roles in cell adhesion events leading to initiation of phagocytosis and encapsulation. Focus will also be made on anti-oxidative enzymes that may participate in the production of reactive oxygen compounds used in the destruction of engulfed or encapsulated parasites. Peroxinectin is stored in semi-granular and granular hemocytes and released concomitant with activation of prophenoloxidase (proPO). It is a cell adhesion protein, enhancing phagocytosis and encapsulation and triggers degranulation. It is also a peroxidase, belonging to the same protein family as mammalian myeloperoxidase. Peroxinectin binds a 90-kDa peripheral cell surface superoxide dismutase (SOD) of crayfish blood cells. Integrins are transmembrane proteins present on crayfish hemocytes and commonly known to be acting as cell adhesion receptors in many events. After its release and activation, peroxinectin may opsonize foreign surfaces where it is recognized by integrins on the hemocyte. This can be a starting point for phagocytosis or encapsulation. Peroxinectin and extracellular SOD (EC-SOD) may then cooperate during a respiratory burst to destroy an ingested or encapsulated parasite.