EFFECTS OF HISTOPLASMIN-M ANTIGEN CHEMICAL AND ENZYMATIC DEGLYCOSYLATION ON CROSS-REACTIVITY IN THE ENZYME-LINKED IMMUNOELECTROTRANSFER BLOT METHOD

The enzyme-linked immunoelectrotransfer blot (EITB) method was evaluat ed as a suitable method for detecting antibodies against M antigen of Histoplasma capsulatum by use of both glycosylated and deglycosylated M protein of histoplasmin (HMIN). Sera from patients with histoplasmos is, paracoccidioidomycosis, blastomycosis, coccidioidomycosis, and asp ergillosis were tested by the EITB with glycosylated M protein of HMIN . This assay demonstrated 100% sensitivity with histoplasmosis serum s amples, all of which reacted with the 94-kDa glycoprotein (M antigen). Although the EITB is highly sensitive, it is not specific for histopl asmosis when glycosylated M protein is used as an antigen. A total of 81% of paracoccidioidomycosis, 25% of blastomycosis, 33% of coccidioid omycosis, 73% of aspergillosis, and 16% of tuberculosis serum samples cross-reacted with M protein of HMIN and yielded patterns indistinguis hable from those obtained with histoplasmosis serum samples. The EITB reactions with both untreated M antigen and M antigen altered by perio date oxidation or by deglycosylation with endoglycosidases were compar ed. Cross-reactions with heterologous sera in the EITB could be attrib uted to periodate-sensitive carbohydrate epitopes, as reflected by the increase in the test specificity from 46.1 to 91.2% after periodate t reatment of M protein. The EITB for the detection of antibodies to M a ntigen is a potential diagnostic test for histoplasmosis, provided tha t periodate-treated M protein is used as an antigen.