Investigation of Specific IgG-Secreting Cells in Congenital Toxoplasmosis: The TOXODIAG Study

Current neonatal diagnostic tests for congenital toxoplasmosis (CT) have limited performance, which is particularly problematic in resource-limited settings and where monitoring for toxoplasmosis during pregnancy is lacking. The TOXODIAG study (NCT03385499) aimed to detect specific IgGs as soon as they appear in pregnant women with acute infection with Toxoplasma gondii (Tg) and their newborns suspected of infection.

Seventy pregnant women were included in five perinatal centers in Paris, France. They were divided into three groups based on their Toxoplasma seroconversion during pregnancy (n = 20, group of interest) and their immune status at delivery with latent infection (n = 23) or confirmed absence of infection (n = 27, control groups). The enzyme-linked immunospot (ELISPOT) method was used to detect B lymphocytes primed to produce IgG against the recombinant antigens TgSAG1, TgGRA7, and TgAMA1.

Complete and validated ELISPOT results were obtained for 9 women in the SEROCO group, including 1 of the 5 CT cases resulting from pregnancy in this group. Tg-specific IgG-secreting cells were observed in mothers at the time of diagnosis of Tg seroconversion and delivery, but not in cord blood. A simplified version of the ELISPOT test, combining the three Tg antigens in a single plate well, reproduced the information provided by the antigens considered independently, with a positivity rate of 35% compared to a range of 6%-37%.

The ELISPOT method could be useful for maternal screening, but for postnatal detection of Tg-specific IgG-secreting cells, it either requires further technical improvements or is not a suitable method.