Anti-P30 IgA antibodies as prenatal markers of congenital toxoplasma infection.

This study extends a previous study and confirms that the detection of anti-P30 IgA antibodies is very helpful in the diagnosis of acute acquired or congenital toxoplasmosis. Moreover, we demonstrate that an anti-P30 IgA response can be mounted in the fetuses infected by Toxoplasma gondii during their intra-uterine life as early as week 23 of gestation. A double-sandwich ELISA described in our previous work was used to detect anti-P30 IgA antibodies in 1378 human serum samples collected from 551 patients, including 162 fetuses whose mothers had been infected by T. gondii during pregnancy, 46 congenitally infected and 90 uninfected newborns and 253 women suspected of having been infected during pregnancy, including the mothers of fetuses and newborns previously described. Anti-P30 IgA antibodies were detected in all cases of acute toxoplasmosis but in no case of chronic toxoplasmosis: in the majority of cases, the IgA antibody titre fell below cut-off in 3-9 months. Among the 46 congenitally infected newborns, anti-P30 IgA antibodies were detected in sera of 41 infected newborns (38 at birth, two in the first months of life, one in the seventh month of life), while anti-P30 IgM antibodies were detected in only 30 cases at birth and in one case during the first month of life. Among 162 fetuses, anti-P30 IgA response was observed in five infected fetuses, but was not detected in either 152 uninfected fetuses or in five fetuses considered as infected. The absence or presence of anti-P30 IgA antibodies in the fetus is discussed in relation to the date of maternal infection and collection of the fetal blood. It clearly appears from our study that the combined testing of both IgM and IgA in the fetus and the newborn is essential for a more efficient diagnosis of infection.