Cell-free antigens of Sporothrix brasiliensis: antigenic diversity and application in an immunoblot assay

Summary Sporotrichosis is a subcutaneous mycosis diagnosed by isolation of the fungus in culture. Serological tests for help in diagnosis in general do not use purified or recombinant antigens, because there is a paucity of described immunoreactive proteins, especially for the new described Sporothrix species, such as Sporothrix brasiliensis. This study aims to characterise antigens from S. brasiliensis and verify their application in serodiagnosis of sporotrichosis. An immunoblot assay allied with computer‐based analysis was used to identify putative antigenic molecules in a cell‐free extracts of both morphological phases of this fungus, and to delineate antigenic polymorphism among seven S. brasiliensis isolates and one S. schenckii Brazilian strain. The mycelial and yeast phase of the fungus originated 14 and 23 reactive bands, respectively, which were variable in intensity. An 85 kDa antigen, verified in the yeast phase of the fungus, was observed in all strains used and the immunodominant protein was identified. This protein, however, cross‐react with serum samples from patients infected with other pathogens. The results show that the S. brasiliensis cell‐free antigen extract is a single and inexpensive source of antigens, and can be applied on the sporotrichosis serodiagnosis.