In pre-treatment cells were treated with 10 μM of the five most effective VDR agonists (ZD-1, ZD-2, ZD-3, ZD-5, and ZD-6) for 6, 3 or 1 h before infection, and after 24 h both the level of infection and the virus titer in the supernatant were determined by flow cytometry and standard plaque assay respectively. Here, VDR is linked to infection.