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Am. J. Trop. Med. Hyg., 72(6), 2005, pp. 831–836 Copyright © 2005 by The American Society of Tropical Medicine and Hygiene

PROTEASE SECRETED BY THE INFECTIVE LARVAE OF ANGIOSTRONGYLUS CANTONENSIS AND ITS ROLE IN THE PENETRATION OF MOUSE INTESTINE
JUNE-DER LEE AND CHUAN-MIN YEN Department of Parasitology, Kaohsiung Medical University, Taiwan

Abstract. The infective third-stage larvae of Angiostrongylus cantonensis secrete a proteolytic enzyme that is thought to be essential for both larval penetration into the intestinal wall of the host and full development. Protease activity in these larvae during culture in vitro was determined by zymography, pH optimum, and substrate and inhibitor specificity. Excretory-secretory (ES) products of the third-stage larvae showed protease activity as three bands with molecular masses of 66, 30, and 23 kD by gelatin zymography. The optimal pH value for this protease activity was 10.0. The protease was found to have collagenolytic as well as elastinolytic activity, but these activities were inhibited by serine protease or metalloprotease inhibitors. The importance of this protease in larval penetration of the intestinal wall and entering the blood stream was observed in vitro by cocultured third-stage larvae of A. cantonensis with specific protease inhibitors in the intestines of BALB/c mice. The penetration rates of larvae significantly decreased when serine protease or metalloprotease inhibitors were added to the intestines. These results showed that serine protease and metalloprotease in ES products of A. cantonensis third-stage larvae are associated with larval penetration of the intestinal walls of mice. INTRODUCTION During the life cycle of Angiostrongylus cantonensis, the infective third-stage larvae (L3) are ingested into the lumen of non-permissive hosts, including humans, migrate via the venous system into the lungs, and then develop into the fifthstage larvae in the brain, inducing diseases such as eosinophilic