CCR7 and infection: However, compared to uninfected mice, CCR7 expression has been shown to be down-regulated on influenza virus-specific CD4+ T cells obtained from the spleen, mesenteric lymph nodes (MLNs) and the lungs at the peak of infection (Debes et al., 2004) (Figure 2), indicating that these cells lost the ability to recirculate after the response to viral antigens (Ags).