This assay has been used as the standard point-of-care laboratory method ever since its discovery by Paul and Bunnell in 1932.11 Paul and Bunnell defined heterophile antibodies as ‘having the capacity to react to certain antigens, which are quite different from, and phylogenetically unrelated to the one instrumental in producing the antibody response.' Heterophile tests use mammalian erythrocytes from various species to detect IgM class antibodies against them, which are raised during the generalized immune upregulation that accompanies acute primary EBV infection. Here, CD40LG is linked to Epstein-Barr virus infection.