In the present study, we analyzed human antibody responses to Paracoccidioides brasiliensis cellular
antigens by the immunoblot technique to identify specific cellular components and to investigate the existence of
antigen profile differences among serological responses of
paracoccidioidomycosis (PCM) patients. Among the 64 PCM serum samples analyzed, a relatively homogeneous
immunoglobulin G response to P. brasiliensis
antigens was observed. The
polypeptide with a mass of 45 kDa was the most clinically important, since antibody to this
antigen was detectable in 90.6% of PCM patients studied and the six individuals who did not produce antibody were either at the end of treatment or in the posttherapy period and had shown clinical recovery. These facts suggested that the presence of this antibody may be an
indicator of active disease. The 45-kDa
antigen was also the most specific
antigen of the PCM humoral immune response, since it reacted with only 2 of 79 (2.5%) heterologous serum samples tested: 1
histoplasmosis case and 1
tuberculosis case. This
polypeptide was isolated from
gels by electroelution and, when tested by an immunoradiometric assay and immunoblotting, maintained its reactivity with PCM sera and also with anti-P. brasiliensis polyclonal
antibodies raised in rabbits at the same sensitivity levels as those obtained in immunoblotting with a crude
antigen. Since in our assays the 45-kDa
polypeptide was the major P. brasiliensis
antigen and seemed to be specific for PCM, its use in alternative diagnostic methods is promising, especially in patients suspected of having the juvenile clinical form of PCM often associated with negative double-immunodiffusion results.