Research Article

Natural anti-proteases in rainbow trout, Oncorhynchus mykiss and brook charr, Salvelinus fontinalis and the in vitro neutralization of fish [alpha]2-macroglobulin by the metalloprotease from the pathogenic haemoflagellate, Cryptobia salmositica

X. ZUO a1 and P. T. K. WOO a1
a1 Department of Zoology, University of Guelph, Guelph, Ontario, Canada N1G 2W1


Natural anti-proteases ([alpha]1-protease inhibitor ([alpha]1-PI; [alpha]1-antitrypsin) and [alpha]2-macroglobulin ([alpha]2-M)) were found in the blood of rainbow trout, Oncorhynchus mykiss and brook charr, Salvelinus fontinalis. The [alpha]2-M inhibited Cryptobia salmositica proteases and was significantly higher in brook charr than in rainbow trout. Under in vitro conditions it took longer for the same number of parasites to neutralize the [alpha]2-M in charr than in trout blood. The haemolysis which occurred when C. salmositica was incubated in the blood of rainbow trout was due to neutralization of [alpha]2-M. This in vitro study also showed that it was the metalloprotease of C. salmositica that lysed red blood cells and the plasma of the two species of fishes initially prevented haemolysis by inhibiting the proteolytic activity. We suggest that the natural plasma [alpha]2-M plays an important role in defence against cryptobiosis in fishes.

(Received August 12 1996)
(Revised September 30 1996)
(Accepted October 2 1996)

Key Words: Cryptobia salmositica; Oncorhynchus mykiss; Salvelinus fontinalis; [alpha]2-macroglobulin; [alpha]1-protease inhibitor; protease.


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