A solid-phase indirect haemadsorption assay (SPIHA) for detection of immunoglobulin m antibodies to Toxoplasma gondii: application to diagnosis of acute acquired toxoplasmosis.

A solid-phase indirect haemadsorption assay (SPIHA) for the detection of immunoglobulin M (IgM) antibodies to Toxoplasma gondii is described. Polystyrol microtiter plates are coated with anti-human IgM (mu-chain-specific) antibodies and then sequentially allowed to react with patient's serum and sheep erythrocytes sensitized with soluble antigen of Toxoplasma gondii. A total of 111 sera were tested in fluorescent antibody test (FAT and IgM-FAT), complement fixation test (CFT), indirect haemagglutination assay (IHA), and in SPIHA. 47 sera were from individuals with a suspected or verified acute Toxoplasma infection. In most of these cases the SPIHA allowed a clear interpretation with respect to the status of the infection, even when the IgM-FAT was not conclusive. In contrast to IgM-FAT, rheumatoid factor or exceedingly high specific IgG antibodies did not interfere with results in SPIHA. A laboratory-acquired infection enabled us to demonstrate the course of immune response measured by SPIHA as well as by IgM-FAT, FAT, CFT, and IHA. The method proposed here is well appropriated to IgM detection, simple to perform, inexpensive, and thus representing an alternative to IgM-FAT, convenient for the routine laboratory.