Application of iscom antigen preparations in ELISAs for diagnosis of Neospora and Toxoplasma infections.

Immunostimulating complexes (iscoms) are cage-like structures of about 40 nm composed of Quil A, cholesterol, phospholipids and antigen. Their main area of use has been as adjuvants and carriers of immunogens in vaccines. Iscoms can also be used for selection of surface membrane proteins of micro-organisms for use in immunoassays, thus decreasing the number of internal proteins that might cause problems with non-specific binding and cross-reactivity. Enzyme-linked immunoassays (ELISAs) utilising parasite antigens incorporated into iscoms have been developed for demonstration of antibodies directed to the intracellular coccidian parasites Toxoplasma gondii and Neospora caninum. These iscom ELISAs have proved very reliable, with high sensitivity and specificity. The preparation of T. gondii and N. caninum iscoms is described, and ELISAs based on iscom antigen preparations that have so far been used for diagnosis of protozoal infections are reviewed.