Immunolocalization of an endogenous antigenic material of Rhinosporidium seeberi expressed only during mature sporangial development

We investigated the immunolocalization of Rhinosporidium seeberi's antigens using sera from individuals infected with ii. seeberi and tissue from Sri Lankan patients with rhinosporidiosis. The tissues were fixed in LR white r esin, thin sectioned, fixed onto nickel grids and evaluated by transmission electron microscopy for the presence of R. seeberi's sporangia. The tissue samples were reacted with the patients's sera and then labeled with protei n A colloidal gold (PACG) for immunolocalization, It was found that the PAC G had fixed to antibodies that specifically recognized an internal electron lucent layer situated immediately under the mature sporangium's wall. Stri kingly, the endospores, the juvenile and intermediate sporangia did not und ergo PACG labeling. This study found that the expression of this antigen oc curs only in the final developmental stages of R. seeberi's mature sporangi a. Our data may explain why circulating antibodies to R. Seeberi were not d etected before in studies that used endospores as antigen in immunoassays. This is the first report in which an antigenic material with a potential ro le in the immunology of rhinosporidiosis has been detected. (C) 1999 Federa tion of European Microbiological Societies. Published by Elsevier Science B .V. All rights reserved.