Encephalocytozoon intestinalis-specific monoclonal antibodies for laboratory diagnosis of microsporidiosis

Two monoclonal antibodies which can be used for the unambiguous identification by fluorescence microscopy of Encephalitozoon intestinalis spores in clinical specimens are described. Monoclonal antibody Si91 is specific for the extruded polar filament, and Si13 recognizes the surfaces of E. intestinalis spores. No cross-reaction with spores of Encephalitozoon hellem was observed. Immunogold electron microscopy confirmed the specific reactivities of both antibodies. Combined in an indirect immunofluorescence assay, these antibodies are used to identify spores in feces. Although there was some cross-reaction with fecal bacteria and fungi, the typical morphology of the extruded polar filaments enabled proper identification of the E. intestinalis spores. Parasites could also be demonstrated to be present in urine, nasal swabs, lung brush biopsy specimens, and bronchoalveolar lavage fluid from a patient with disseminated infection with E. intestinalis. The use of these monoclonal antibodies facilitates the detection and species determination of E. intestinalis in clinical specimens.