Toxoplasma gondii: enzyme-linked immunosorbent assay based on a recombinant multi-epitope peptide for distinguishing recent from past infection in human sera.

Enzyme-linked immunosorbent assays (ELISAs) based on a recombinant multi-epitope peptide (rMEP) were used in an attempt to differentiate pregnant women with Toxoplasma serologic profiles (TSPs) indicative of recently acquired infections (acute profile) from those with TSPs indicative of infections acquired in the distant past (chronic profile). The recombinant expression vector pET-32c-MEP encoding MEP constructed previously was expressed in Escherichia coli and the rMEP was purified as a bioactive fusion protein. The IgG-ELISA and IgM-ELISA based on the purified rMEP were developed, and used to detect IgG and IgM antibodies against Toxoplasma gondii in human sera. Immunoblot assays showed that the purified rMEP could be strongly recognized by IgM antibodies in the pooled sera from women with acute profiles, and by IgG antibodies in the pooled sera from women with chronic profiles. ELISA results also proved that the reactivities of IgG and IgM antibodies differed significantly in sera from women with acute and chronic profiles. Compared with two commercial ELISA tests for seradiagnosis of toxoplasmosis, the total concordance (including positive and negative sera) of this rMEP-based assay was 93.2% and 95.7% for the detection of IgG and IgM antibodies, respectively. Our study suggests that the rMEP protein could be used as the diagnostic antigen to differentiate recent from past infections in human toxoplasmosis.