The luciferase activity in CEM.NKR CCR5 luc cells, a surrogate marker of infection, was reduced only when both the positive-control anti-SIV Env monoclonal antibody (MAb) B404 (40) and KHYG-1 cells were present, indicating that the system was appropriate for assessing ADCC (data not shown). Here, CCR5 is linked to infection.