Heat Shock Proteins and Disease Control in Aquatic Organisms

Abstract

Four families of heat shock proteins (Hsps), including the small heat shock proteins (sHsps), Hsp70, Hsp90 and Hsp60, are synthesized under normal physiological conditions and in response to stress. sHsps protect proteins from irreversible denaturation independently of ATP. The remaining ATP-responsive Hsps fold nascent proteins, shield proteins from irreversible denaturation during stress and aid protein refolding. Several observations indicate that Hsps contribute to disease resistance in aquatic organisms, the first being that these proteins are produced in finfish, shellfish and bivalves upon infection with viral and bacterial pathogens. Induction of Hsp synthesis by heat shock and incubation with chemicals such as Pro-Tex® boosts resistance to pathogens, as does administration of exogenous Hsps to host organisms. The extent of Hsp accumulation and the increase in disease tolerance are generally correlated with one another. Not only do Hsps protect against pathogens by functioning as molecular chaperones, but they are thought to mediate humoral and cellular innate immune responses. Hsp70 is highly immunogenic and serves as a ligand for Toll-like receptors. Hsps elicit cytokine production and they deliver peptides to antigen presenting cells via major histocompatibility complexes (MHC). Vaccines have been produced for use in aquaculture by employing Hsps, either alone or fused to antigens obtained from pathogens. Hsps offer several advantages over current methods for the treatment of disease in commercially important organisms and they are being increasingly exploited as their roles in protein chaperoning and immune modulation are better understood.