Immunoglobulin-A detection and the investigation of clinical toxoplasmosis.

Current serological methods for the investigation of Toxoplasma gondii infection are unreliable for the diagnosis of congenital disease, reactivated infection associated with the acquired immune deficiency syndrome (AIDS), or the determination of the date of onset of infection. An enzyme-linked immunosorbent assay (ELISA) and an immunosorbent agglutination assay (ISAGA) were developed for the detection of toxoplasma-specific immunoglobulin-A (IgA) and used to investigate patients in these three categories. The IgA ISAGA and IgA ELISA were found to be reproducible and specific tests. The IgA ISAGA demonstrated enhanced sensitivity. Measurement of IgA in patients with toxoplasma-associated lymphadenopathy of known duration and AIDS patients with toxoplasma infection was of limited value. Detection of specific IgA by ISAGA was more sensitive than conventional methods for the diagnosis of congenital toxoplasmosis. We recommend the investigation of infant sera with IgA ISAGA. IgA estimation is not indicated in other clinical situations.