Schistosoma mansoni proteases Sm3l (cathepsin B) and Sm32 (legumain) are expressed in the cecum and protonephridia of cercariae

Adult Schistosoma mansoni parasites live in the bloodstream of their verteb rate hosts where they consume red blood cells. Hemoglobin, released from th e ingested red blood cells, is degraded by a variety of parasite proteases, including Sm31 (cathepsin B) and Sm32 (schistosome legumain). In this stud y the localization pattern of the Sm31 and Sm32 enzymes in cercariae (the i nfectious life cycle stage) was examined. Antibodies generated against reco mbinant Sm31 and Sm32 recognize their respective proteins in Western blots of soluble parasite extracts. Highest levels are seen in adult female extra cts, whereas the level of both proteins is below detection in cercarial ext racts. However, in fixed, whole cercariae, both proteins are seen in the ce cum and protonephridia. In the cecum, the staining pattern has a granular a ppearance, suggesting that the proteins are packaged in vesicles. In the pr otonephridial system, Sm31 and Sm32 are detected in all 8 flame cells in th e cercarial body and in both flame cells in the cercarial tail. The distrib ution of the 2 proteins differs in the flame cells. Examination of immunost ained cercariae using laser scanning confocal microscopy shows that whereas Sm31 is located in the tubule cell, Sm32 is found in both the tubule cell and its adjoining cap cell. These findings suggest that the proteins are in volved in the proposed excretory and osmoregulatory roles of flame cells.