CONGENITAL AND NEONATAL SYPHILIS IN GUINEA-PIGS SHOW A PATTERN OF IMMUNE-RESPONSE

C4-deficient (C4D) and Albany strains of guinea-pigs transplacentally and neonatally infected with Treponema pallidum showed distinctive pat terns of humoral immune responses. Congenitally infected progeny of bo th strains originated from dams intradermally (i.d.) infected at midpr egnancy with virulent T. pallidum. In the neonatal groups families of C4D and Albany strains consisting of 1-3-day-old offspring and their m others were i.d. infected with a similar dose of T. pallidum. Regardle ss of the strain, asymptomatic congenitally infected guinea-pigs (n = 16) responded from the first day of life with high levels of IgM [T. p allidum (TP) ELISA] antitreponemal antibodies and up to 85% presented with IgM CIC (circulating immune complexes) and IgM RF (rheumatoid fac tor). Although relatively high levels of IgM antitreponemal antibodies persisted in these animals throughout the 4-month experimental period , significant levels of host IgG antitreponemal antibodies were detect able after 2-3 months of age. Neonatally infected guinea-pigs of both strains (n = 27) responded similarly to the infected sow but with rela tively lower levels of IgM and IgG antitreponemal antibodies at 1 and 4 weeks, respectively, both of which increased with the time of infect ion. Antibodies were also detected in these animals by fluorescent tre ponemal antibody adsorption test (FTA-ABS). Unlike congenital syphilis , neonatally infected animals developed IgG-CIC after 2-3 months of in fection and none of them showed any RF. In neonatal syphilis, FTA-ABS antibody levels were closely associated with the onset of lesions, whe reas those of TP ELISA were not. The distinctive immune responses obse rved in these experimental models have the potential to differentiate between congenitally and neonatally infected human infants, even thoug h the current clinical management is the same.