Identification of the microsporidian Encephalitozoon hellem using immunoglobulin G monoclonal antibodies

Objective.-Microsporidia isolated from clinical specimens so far have been identified to level of species by electron microscopy, indirect immunofluorescence (IIF), western blot (WE), and genetic analysis. Recent studies, however, indicate extensive serologic cross-reactions among microsporidian species involved in human disease. Design and Setting.-In this study, we used IIF and WE techniques to evaluate the reactivity of six different immunoglobulin G monoclonal antibodies (MAbs) raised against Encephalitozoon hellem with six isolates of E hellem that originated from patients with acquired immunodeficiency syndrome. A rabbit isolate of Encephalitozoon cuniculi, and an isolate of Encephalitozoon intestinalis, which was established in cultures from the urine of a patient with acquired immunodeficiency syndrome were also used for comparison. Results.-Five of the six antibodies, when analyzed by both IIF and WE assays, specifically identified six isolates of E hellem originating from three patients with acquired immunodeficiency syndrome. The sixth MAb, however, reacted with all of the E hellem isolates in the WE assay, but failed to react with them in the IIF assay. Using the IIF test, five of the six MAbs failed to react with E cuniculi and E intestinalis, even at a dilution of 1:50. The MAbs also did not read in the IIF test with Enterocytozoon bieneusi, Giardia, and Cryptosporidium. These MAbs did react with E cunicoli and E intestinalis in the WE assay, but the banding patterns were very different from those of E hellem, thus facilitating the identification of E hellem from the other microsporidia. The MAbs also reacted, in the IIF test, with E hellem spores in formalin-fixed tissue sections that were heated in a microwave oven. Conclusions.-Identification of microsporidian agents to the species level is important. Since certain therapeutic agents (eg, fumagillin, albendazole) are efficacious in treating E hellem infections of the cornea, as well as urogenital and respiratory infections caused by E hellem, a quick and definitive identification of the organism is important so that successful therapy may be instituted. An IIF test using the MAbs described here would therefore be invaluable in the quick identification of this parasite.