NATURAL ANTI-PROTEASES IN RAINBOW-TROUT, ONCORHYNCHUS-MYKISS AND BROOK CHARR, SALVELINUS-FONTINALIS AND THE IN-VITRO NEUTRALIZATION OF FISHALPHA-2-MACROGLOBULIN BY THE METALLOPROTEASE FROM THE PATHOGENIC HEMOFLAGELLATE, CRYPTOBIA-SALMOSITICA

Natural anti-proteases (alpha 1-protease inhibitor (alpha 1-PI; alpha 1-antitrypsin) and alpha 2-macroglobulin (alpha 2-M)) were found in th e blood of rainbow trout, Oncorhynchus mykiss and brook charr, Salveli nus fontinalis. The alpha 2-M inhibited Cryptobia salmositica protease s and was significantly higher in brook charr than in rainbow trout. U nder in vitro conditions it took longer for the same number of parasit es to neutralize the alpha 2-M in charr than in trout blood. The haemo lysis which occurred when C. salmositica was incubated in the blood of rainbow trout was due to neutralization of alpha 2-M. This in vitro s tudy also showed that it was the metalloprotease of C. salmositica tha t lysed red blood cells and the plasma of the two species of fishes in itially prevented haemolysis by inhibiting the proteolytic activity. W e suggest that the natural plasma alpha 2-M: plays an important role i n defence against cryptobiosis in fishes.