Membrane and extracellular antigens of Paracoccidioides brasiliensis (Mexo): identification of a 28-kDa protein suitable for immunodiagnosis of paracoccidioidomycosis.

In this work, we analyzed serological responses of paracoccidioidomycosis (PCM) patients to membrane and extracellular antigens (Mexo) of Paracoccidioides brasiliensis by ELISA, immunoblot technique and immunofluorescence assays to identify a specific antigen profile. Among 140 PCM serum samples analyzed, a homogeneous IgG response to Mexo was observed. The specificity of this antigen was 96.6% in relation to control sera and 81.2% to sera from patients with diverse infections. Patients undergoing treatment for more than 1 year showed a reduced antibody response against Mexo. These results suggest that the presence of anti-Mexo antibodies might be an indicator of active disease. A protein from Mexo with a molecular weight of 28 kDa (Pb28) was the most specific antigen in humoral immune responses to PCM, since it reacted with 100% of patient sera and did not react with heterologous serum samples tested. This protein was purified by molecular filtration chromatography in FPLC system and, when tested by immunoblotting, it maintained its reactivity and specificity of 100% with PCM sera. The Pb28 N-terminal amino acid sequence comparison analysis in the non-redundant GenBank database at NCBI revealed no significant homology to known PCM proteins or to other fungal proteins of known function. Since the 28-kDa protein of P. brasiliensis seems to be specific for PCM, it can be used as an alternative antigen in immunoblotting diagnostic methods.