An 80-kilodalton Trypanosoma cruzi
antigen is eliminated in the urine of infected hosts during the acute stage of
Chagas' disease. We show that affinity-purified urinary
antigen is recognised by
IgM antibodies in the sera from acute chagasic patients. Comparing our urinary
antigen assay with that using a whole T. cruzi lysate
antigen for
IgM antibody detection, we demonstrated that ELISA with urinary
antigen increases the diagnostic sensitivity and specificity of
IgM serology in recent chagasic
infection. Twenty-six of 30 patients with acute T. cruzi
infection had serum
IgM antibodies that reacted with urinary
antigen by ELISA, while lysate
antigen IgM was detected in 24 sera. When sera from patients suffering other parasitoses were tested, strong cross-reactions occurred in ELISA with T. cruzi lysate
antigen, whereas ELISA with urinary
antigen proved to better discriminate acute chagasic patients. Human
antibodies to urinary
antigen immunoprecipitated this T. cruzi urinary
antigen and also inhibited the binding of
monoclonal antibody to urinary
antigen in an inhibition assay. These findings suggest that urinary
antigen may be useful for the development of serodiagnostic procedures for acute T. cruzi
infection.