The acute phase response and innate immunity of fish

Tissue trauma or invasion by pathogens or parasites induce changes in the q uantities of several macromolecules in animal body fluids. These changes co mprise one aspect of the acute phase response (APR), which in toto involves metabolic changes in several organ systems. One clear indication of the re sponse is the increase in synthesis and secretion by the liver of several p lasma proteins, with simultaneous decreases in others. These acute phase pr oteins (APP) function in a variety of defense-related activities such as li miting the dispersal of infectious agents, repair of tissue damage, inactiv ation of proteases, killing of microbes and other potential pathogens, and restoration of the healthy state. Some APP are directly harmful to microbes , while others modify targets thus marking them for cell responses. Some wo rk alone while others contribute to cascades. Proteins that are APP in mamm als, and that have been identified in both teleosts and elasmobranchs inclu de C-reactive protein, serum amyloid P, and several components of the Compl ement system. Others reported in teleosts include transferrin and thrombin. Of these, only CRP has been reported to increase in acute phase plasma. In trout, a precerebellin-like protein is an APP with unknown functions. A cD NA library enriched in fragments of transcripts that were more abundant in livers from fish undergoing an APR recently yielded sequences resembling 12 additional known APP, and as many others either not known to be APP, or no t similar to others yet in public databases. It appears that, as in mammals , hepatocytes are the prime source of APP in fish, and that pro-inflammator y cytokines induce transcription of their genes. (C) 2001 Elsevier Science Ltd. All rights reserved.