Schistosoma japonicum: immunocytochemistry of adults using heterologous antiserum to bovine cathepsin D.

Results from previous biochemical and cytochemical studies show that a pepstatin-sensitive hemoglobinase is present in the gastrodermis of adult Schistosoma japonicum. To determine whether there is structural similarity to mammalian cathepsin D in addition to inhibition similarity, an immunocytochemical study was initiated using heterologous antiserum to bovine cathepsin D. With light microscopy, immunostaining was observed in the cecal lumen, the gastrodermis, and on the dorsal tegument and tubercles of male worms. With transmission electron microscopy, immunostaining was observed in gastrodermal autophagosomes and tegumental invaginations of the dorsal tegument of males. Immunostaining was also observed within the tubercles, but the reaction product did not appear to be associated with any definite structure or organelle. Heavy endogenous peroxidase activity in the cecal lumen due to ingested hemoglobin obscured with immunostaining. Assuming that all immunostaining is due to molecules that function in a manner similar to that of cathepsin D, it is suggested that such molecules may regulate some aspect of the host-parasite relationship and/or the parasite's metabolism. Alternatively, the immunostained molecules may be structural proteins with epitopes similar to those of mammalian cathepsin D. Reactions associated with the cecum, however, on the basis of previous studies, are believed to derive from molecules that are proteolytic enzymes.