Recognition of Treponema pallidum antigens by IgM and IgG antibodies in congenitally infected newborns and their mothers.

Immunoblotting techniques were used to examine the proteins of Treponema pallidum recognized by IgM and IgG antibodies in sera from infants with congenital syphilis and their mothers. Infected infants' serum IgM reactivity to treponemal antigens differed from that of control infants born to normal, serofast, and biologic false-positive mothers. Each of the infected infants' sera exhibited IgM reactions to the 47- and 37-kilodalton (kDa) proteins of T. pallidum. Although rheumatoid factor was detected in the sera of half of the infected infants, removing this factor did not alter the pattern of IgM blots. IgG reactions in infants were almost exclusively of the IgG1 and IgG3 subclasses and mirrored those of the mother, except for IgG1 and IgG3 reactions to the 83-kDa treponemal protein, which were unique to infants' sera. Our results suggest that the findings of IgM antibody directed against the 47- or 37-kDa antigens of T. pallidum may help to diagnose congenital syphilis at birth.