CD80 and infection: To evaluate the extent of this phenomenon, HeLa instead of DF1 cells were infected with different poxviruses (Fig. 2 and legend) at a high multiplicity of infection (MOI) (i.e., an MOI of 1) to guarantee an optimal infection and expression of viral proteins by infected cells, and the resulting culture supernatants were tested in a CD80-CTLA4 ELISA.