Heterophile specificity is determined by the presence of
heterophile antigens. The same or closely related antigens, sometimes present
in tissues of different biological spe-cies, classes, or kingdoms are known as heterophile
antigens. Antibodies against the heterophile antigens produced by one
of the species cross-react with the antigens of other species. This property is
exploited for diagnosis of many infectious diseases. Weil–Felix reaction,
Paul-Bunnell test, and cold agglutination tests are the examples of serological
tests that use such heterophile antigens.