Signaling molecules involved in immune responses in mussels

Abstract

Immune system of molluscs is constituted by hemocytes and humoral factors that cooperate for the protection of the organism, triggering a wide range of immune responses. In molluscs, immune responses include phagocytosis, encapsulation, respiratory burst leading to reactive oxygen species (ROS) production and nitric oxide (NO) synthesis, release of antimicrobial molecules and the activation of phenoloxidase system. These responses are mediated firstly by a variety of hemocyte receptors binding to ligands that results to a cascade of signaling events. The processes of hemocytes adhesion to and migration through extracellular matrix (ECM) proteins play a crucial role in cell immunity. Results suggest that cadmium and oxidants induce adhesion to and migration through ECM proteins in Mytilus gallorovincialis hemocytes with the involvement of Na+ /H+ exchanger (NHE), phosphatidylinositol-3 kinase (PI-3K), protein kinase C (PKC), NADPH oxidase, ROS and NO as well as with α2 integrin subunit. Furthermore, the data so far suggests the involvement of additional signaling molecules such as mitogen-activated protein kinases (MAPKs), signal transducers and activators of transcription (STATs), c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), cyclic adenosine monophosphate (cAMP), responsive element binding protein (CREB) and nuclear factor kappa B (NF-kB) in molluscs immunity. Further research in mollusc immune system may lead to a more sufficient protection and to a better control of these economically important organisms.