Recognition of Toxoplasma gondii excreted and secreted antigens by human sera from acquired and congenital toxoplasmosis: identification of markers of acute and chronic infection.

While the serological response to somatic antigens of Toxoplasma gondii is currently analysed, little information is available on the antibody response to the antigens excreted and secreted by tachyzoïtes (ESA). This serological study is focused on the immune response towards these antigens which were released by the parasites in cell-free culture medium. Human sera corresponding to 'acute', 'subacute' and 'chronic' acquired infection and sera from infected newborns and from their mothers were analysed by radio-immunoprecipitation with 35S methionine-labelled ESA and with radio-iodinated membrane antigens followed by polyacrylamide gel electrophoresis. In chronic toxoplasmosis, IgG antibodies recognized among ESA major 108, 97, 86, 60, 57, 42, 39 and 28.5 kD antigens; the 108-97 kD doublets and the 28.5 kD antigen seemed characteristic of the chronic phase of toxoplasmosis. In acute infection, IgM antibodies to the 97 kD antigen, the first to appear, seem to contitute good markers of early acute infection. The comparative study of antibody response to membrane antigens showed that, in chronic toxoplasmosis, human sera recognized four antigens of 43, 35, 30 and 22 kD and that, in acute toxoplasmosis, they first recognized the 43 and 30 kD antigens. The serological evolution in congenital toxoplasmosis was the same as in acquired infection. In some cases, the serological profile of the newborn was different from that of his mother, with an additional antibody response to a 170 kD antigen. This study demonstrates in human toxoplasmosis an early, intense and characteristic antibody response against ESA, suggesting that the use of these antigens could lead in the future to improved diagnostic tests.