The role of phagocytes in the protective mechanisms of fish

Abstract

Phagocytes are cells principally dedicated to the recognition and elimination of invading organisms and damaged tissue. Those described in fish are the granulocytes (particularly neutrophils) and mononuclear phagocytes (tissue macrophages and circulating monocytes). Their movement to sites of microbial invasion is an early event in the inflammatory response and the role of host-derived factors as attractants, such as eicosanoids, is discussed. Opsonins mediate the recognition between phagocyte and particle, and receptors for serum complement component C3 and the Fc fragment of opsonic antibody have been described. Fundamental to the protection offered by the phagocytes is their bactericidal larvacidal activity, which is closely associated with the production of oxygen free radicals. Phagocytes as accessory cells are discussed, including their role in antigen presentation. A knowledge of the modulation of phagocyte function, with activation by various substances and suppression by others, is important if protective responses are to be achieved by up-regulating phagocyte activity.