CAT and infection: CAT expression was measured by ELISA 6, 12 and 24 h post-infection and, as shown in Figure 1C, it was readily detected by ELISA at 12 h after infection, even at the lowest MOI of 0.1, in cells infected with HSV1-Tat, but not in cells infected with HSV1-LacZ or in uninfected cells, demonstrating that the recombinant HSV1-Tat vector expresses a functionally active Tat protein generated by the recombinant HSV1-Tat.