Plasma proteomic analysis of the acute phase response of rainbow trout (Oncorhynchus mykiss) to intraperitoneal inflammation and LPS injection.

Few acute phase proteins are known in fish and better knowledge of them would provide a basis for more reliable methods to objectively assess fish health and welfare. An acute phase response was induced in rainbow trout (Oncorhynchus mykiss, Walbaum) by inflammation triggered by intraperitoneal administration of purified Aeromonas salmonicida lipopolysaccharide emulsified in Freund's incomplete adjuvant (LPS/FIA) or a commercial oil-based multivalent vaccine. Acute phase proteins were characterized by comparative densitometry of plasma proteins separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and identified by MALDI-TOF and ESI MS/MS mass spectrometry. In one experiment, plasma samples were compared between treatment and control groups in which fish were terminally bled. In another experiment, individual fish were sampled repeatedly. Proteins scored as increased were those whose normalized value increased three-fold or greater between pre- and post-stimulus. Proteins scored as decreased were those whose normalized values decreased two-fold or greater. Unaltered proteins were those that were not altered or did not meet either of these criteria. Proteins that were absent in pre-stimulus gels but present in post-stimulus profiles were considered to be induced. Only those proteins that were altered in all fish for a given treatment were considered. In both experiments, protein p36 was increased up to 13-fold and several proteins were detected that had not been previously. In all fish treated with LPS/FIA, p9.5 was consistently increased an average of 75-fold in plasma. We have constructed a plasma protein panel of eight increased or induced proteins (p9.5, p10.5, p24a, p24b, p24c, p25a, p36 and p37), one decreased (p16) and two that are unaltered (p28a, p28b) in rainbow trout following inflammation or injection with LPS/FIA. Proteins from this panel that were similar to previously identified proteins were pre-cerebellin-like (p24a), transferrin (p37) and apolipoprotein (p10.5, p24c and p28).