The main objective of this work was to improve the early serologic diagnosis of
toxoplasmosis in children at risk of congenital
infection by using recombinant
antigens. Serum samples from 104 infants born to mothers with primary
Toxoplasma gondii infection acquired during pregnancy, of which 35 were congenitally infected and 22 had clinical silent
toxoplasmosis at birth, were included.
Immunoglobulin M (
IgM),
IgG, and
IgG subtype
antibodies against
epitopes carried by fragments of T. gondii MIC2, MIC3, MIC4, M2AP, AMA1, and SAG1 gene products were measured by performing parallel
enzyme immunoassays (Rec-ELISAs). Recombinant
antigens preferentially reacted with
IgG antibodies from infected infants compared to uninfected subjects (P < 0.0001), indicating that sera from infected children recognized a more diverse repertoire of
antigens than sera transferred over the placenta from the mothers. Using two serial samples collected within 3 months of life, it was possible to demonstrate a neosynthesis of specific anti-MIC2 and anti-SAG1
immunoglobulin G, mainly of the
IgG2 subtype, in 13 out of 20 infants with
congenital toxoplasmosis.
IgM antibodies in 97% of infected infants reacted with at least one of the recombinant
antigens, confirming the diagnosis of congenital
infection as soon
as 2 months after birth (P < 0.0001). The use of recombinant
antigens is effective in distinguishing T. gondii-infected from uninfected infants and shows that assays based on recombinant
antigens improve the diagnosis of newborns with
congenital toxoplasmosis.