MKI67 and infection: Higher numbers of IFNγ-expressing CD4+ T cells (Figure 4A) and higher frequencies of proliferating (Ki-67+) CD4+ T cells (Figure 4B) were nonetheless observed after viral antigen stimulation in the SGs of Cd4Cre/+Arg1flox/flox versus Cd4+/+Arg1flox/flox mice during the chronic phase of infection with MCMV.