Detection of immunoglobulin m antibodies to p35 antigen of Toxoplasma gondii for serodiagnosis of recently acquired infection in pregnant women

We examined the efficiency of detection of immunoglobulin M (IgM) antibodie s to a 35-kDa antigen (P35) of Toxoplasma gondii for serodiagnosis of acute infection in pregnant women. A double-sandwich enzyme-linked immunosorbent assay (ELISA) with recombinant P35 antigen (P35-IgM-ELISA) was used for th is purpose. On the basis of the clinical history and the combination of res ults from the toxoplasma serological profile (Sabin-Feldman dye test, conve ntional IgM and IgA ELISAs, and the differential agglutination test), the p atients were classified into three groups: group I, status suggestive of re cently acquired infection; group II, status suggestive of infection acquire d in the distant past; group III, status suggestive of persisting IgM antib odies. Eighteen (90.0%) of 20 serum samples from group I patients were posi tive by the P35-IgM-ELISA whereas none of the 33 serum samples from group I I patients were positive. Only 4 (25.0%) of 16 serum samples from group III patients were positive by the P35-IgM-ELISA, whereas all these serum sampl es were positive by the conventional IgM ELISA, These results indicate that demonstration of IgM antibodies against P35 by the P35-IgM-ELISA is more s pecific for the acute stage of the infection than demonstration of IgM anti bodies by the ELISA that uses a whole-lysate antigen preparation, Studies w ith sera obtained from four pregnant women who seroconverted (IgG and IgM a ntibodies) during pregnancy revealed that two of them became negative by th e P35-IgM-ELISA between 4 and 6 months after seroconversion, whereas the co nventional IgM ELISA titers remained highly positive. The P35-IgM-ELISA app ears to be useful for differentiating recently acquired infection from thos e acquired in the distant past in pregnant women.