To assess the effect of Ad5hr infection on CD4+ regulatory T cells, we evaluated the frequency of CD4+ Treg (Foxp3+/CD25hi) and a CD4+ Treg subset expressing CTLA4 (Foxp3+/CTLA4+/CD25hi) that is thought to be particularly immunosuppressive, as CTLA4 is required for suppression by Tregs [35]. Here, CTLA4 is linked to infection.