Immunoelectron microscopical localization of a circulating antigen in the excretory system of Schistosoma mansoni. Ultrastructural localization studies of the excretory system of S. mansoni

The schistosome excretory system: a key to regulation of metabolism, drug excretion and host interaction

There is a gulf between the enormous information content of the various genome projects and the understanding of the life of the parasite in the host. In vitro studies with adult Schistosoma mansoni using several substrates suggest that the excretory system contains both P-glycoproteins and multiresistance proteins. If both these families of protein were active in vivo, they could regulate parasite metabolism and be responsible for the excretion of drugs. During skin penetration, membrane-impermeant molecules of a wide range of molecular weights can be taken into the cercaria and schistosomulum through the nephridiopore, through the surface membrane or through both. We speculate that this uptake process might stimulate novel signalling pathways involved in growth and development.

Three-dimensional reconstruction of the distribution of flame cells in a trematode cercaria

In order to reveal the vertical distribution of flame cells in a trematode cercaria, horizontal serial semi-thin sections were reconstructed by an image analyzer and a manual procedure. The ascending main excretory tubes extended forward, meandering up and down at the digestive system level from the excretory bladder. At the posterior end of the ventral sucker, they curved dorsally, passed through the dorsal side, returning to the mid level at the anterior end of the ventral sucker. They then ran forward to the posterior part of the oral sucker, and turned back. The flame cells were more abundant in the ventral region than in the dorsal region. The majority of pairs of right and left flame cells were present at the same distance from the digestive system or ventral (or dorsal) surface. This method, using conventional techniques, has some advantages for determining the horizontal and vertical distributions of flame cells in cercaria and may, therefore, promote research on cercaria.

Schistosome glycoconjugates in host-parasite interplay

Schistosomes are digenetic trematodes which cause schistosomiasis, also known as bilharzia, one of the main parasitic infections in man. In tropical and subtropical areas an estimated 200 million people are infected and suffer from the debilitating effects of this chronic disease. Schistosomes live in the blood vessels and strongly modulate the immune response of their host to be able to survive the hostile environment that they are exposed to. It has become increasingly clear that glycoconjugates of schistosome larvae, adult worms and eggs play an important role in the evasion mechanisms that schistosomes utilise to withstand the immunological measures of the host. Upon infection, the host mounts innate as well as adaptive immune responses to antigenic glycan elements, setting the immunological scene characteristic for schistosomiasis. In this review we summarise the structural data now available on schistosome glycans and provide data and ideas regarding the role that these glycans play in the various aspects of the glycobiology and immunology of schistosomiasis.

Immunohistochemical and ultrastructural localization of Schistosoma mansoni soluble egg antigens processed by the infected host

The detection of egg-derived antigens in the serum and urine of Schistosoma mansoni-infected individuals and experimental animals would provide an alternative method to assess the tissue egg burden. The detected levels are, however, not only a function of the amounts of antigen produced, but also of the processing or clearance by the host. In the present study the immunolocalization pattern of antigens using 2 recently described monoclonal antibodies to repetitive carbohydrate epitopes of S. mansoni soluble egg antigen (114-5B1-A and 114-4D12-A) in various organs of the host was investigated. In the liver strong immunoreactivity could be detected around the entrapped eggs and in egg-shells, as well as in Kupffer cells accumulating both antigen and schistosomal pigment. In the spleen, immunohistochemistry revealed antigen in the plasma as well as in secondary lysosomes of macrophages. Strong labelling was found in the vesicles of the eosinophilic granulocytes: indirect evidence perhaps for the presence of antigen-antibody complexes. In conclusion, the secreted egg antigens were sequestered in the reticulo-endothelial macrophages of the liver and the spleen as already partly described for worm-derived antigens. The presence of large quantities of antigenic material in the spleen could suggest an important role of this organ in the clearance of antigen and might even provide an additional explanation for the hepatosplenomegaly mainly present in S. mansoni-infected children.