Role of specific immunoglobulin E in diagnosis of acute toxoplasma infection and toxoplasmosis.

Toxoplasma immunoglobulin E (IgE) antibodies were evaluated in an immunosorbent agglutination assay (ISAGA) and an enzyme-linked immunosorbent assay (ELISA) to determine their usefulness in the diagnosis of acute infection with Toxoplasma gondii. IgE antibodies were not detected in serum specimens from otherwise seronegative individuals, individuals with chronic toxoplasma infection, or infants without congenital toxoplasmosis. In contrast, they were detected in pregnant women who seroconverted during gestation (100% by ELISA, 63% by ISAGA), patients with toxoplasmic lymphadenopathy (96% by ELISA, 88% by ISAGA), infants with signs of congenital toxoplasmosis which prompted serologic testing in the postnatal period (92% by ELISA, 67% by ISAGA), children and adults with toxoplasmic chorioretinitis (36% by ELISA, 18% by ISAGA), and adult patients with AIDS and toxoplasmic encephalitis (33% by ELISA, 25% by ISAGA). In many of the serum specimens, the titer of IgE antibodies detected by the ISAGA were close to or at the positive cutoff value. The duration of detectable IgE antibodies in patients with acute infections varied considerably among individuals but showed a trend toward a briefer duration by the ISAGA than by the ELISA. These results reveal that recrudescence of IgE antibodies in patients with reactivated chronic infection (toxoplasmic chorioretinitis and toxoplasmic encephalitis) may be useful diagnostically and that demonstration of toxoplasma IgE antibodies is a useful adjunct to currently available serologic tests for the diagnosis of acute toxoplasma infection and toxoplasmosis.