Role of Cathepsin B in Schistosoma japonicum Infection

roteases, including cysteine-, serine-, threonine-, aspartate-, and metallo-proteases, are a group of enzymes that have the catalytic ability to hydrolyze or digest peptide bonds of proteins. Proteases play important roles in host invasion, hemoglobin degradation, transformation and immune invasion of schistosomes. The gut cathepsin B of all schistosomes including S. japonicum, S. mansoni and S. haematobuim is involved in hemoglobinolysis. Since Schistosoma japonicum cercariae show quicker migration through host skin as compared to S. mansoni and S. haematobium, it has been proposed that cathepsin B residing in the acetabular gland of S. japonicum might be one of the factors that facilitates its rapid skin penetration. This review focuses on the potential roles of cathepsin B for hemoglobin degradation and skin penetration of schistosomes. Defining the role of cathepsin B might be useful in identifying the drug target for schistosomiasis. Keyword: Schistosoma japonicum, cathepsin B, skin penetration Corresponding: Tan-ariya P. (peerapan.tan @mahidol.ac.th) lungs. In the lungs, the schistosomules undergo developmental changes into young adults. Then, young adults move to the liver where they feed on red blood cells, develop into an adult worm and find a partner. After pairing-up, male and female worms migrate in pairs to the mesenteric vein of the small intestine for egg production. The eggs penetrate to lumen of intestines via small venules and are passed to the external environment in the feces [1]. For initiation of the host penetration process, the cercariae attach to the host skin using their ventral suckers. The schistosome cercariae have a particular head organ in the anterior part that can extend and pull back slightly. The head organ of cercariae has three types of gland cells where secretory vesicles are found: the acetabular gland; the head gland; and the sub-tegumental Mechanisms of host penetration in schistosomes Three major schistosomes, Schistosoma mansoni, S. japonicum and S. haematobium, are the blood parasites of humans and all have a complex life cycle, i.e., snail intermediate host is required in addition to its definitive host. For S. japonicum, humans and other definitive hosts are infected by cercariae which are shed from freshwater snail intermediate hosts. The cercariae in water infect the host by direct skin penetration and rapidly transform into schistosomules, a larva stage, in the blood circulation. It takes several days for the cercariae to pass through the skin, enter the blood vessels and migrate to the heart and the Available online at http://www.tm.mahidol.ac.th/ptat Vol. 37 (No. 2) December 2014 T H E JO U R N A L O F T R O IC A L M ED IC IN E A N D PA R A IT O LO G Y