Antibacterial proteins in rainbow trout, Oncorhynchus mykiss

Antibacterial proteins are an important part of the innate immune system fo r all animals. They have been extensively studied in mammals, amphibians an d invertebrates, but have received only scant attention in fish. Their expr ession and processing, however, provide a way of monitoring defence vigour during development or with seasonal changes in physiology. The aim of the p resent work was to identify and characterise antibacterial proteins in rain bow trout. In vitro analyses of extracts of the peripheral blood leucocytes , head kidney leucocytes and mucus from adult unstimulated (non-immune) fis h showed marked antibacterial activity against Gram positive bacteria. Frac tionation by ion exchange chromatography and RP-HPLC of head kidney extract s showed the presence of two forms of lysozyme but no constitutively expres sed antimicrobial proteins of <10 kDa. By contrast, chromatographic analyse s of mucus revealed at least four antibacterial proteins. Two are conventio nal lysozymes, a third is an unusual lysozyme-like protein with a low isoel ectric point, and the fourth is a highly hydrophobic, cationic peptide of c . 3 kDa. (C) 2000 Academic Press.