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.