IFITM3 and lymphopenia: Remarkably, using the murine CMV (MCMV) model of infection, it has been shown that although IFITM3 does not restrict MCMV replication, IFITM3 deficiency leads to an impairment of cellular immunity most likely due to an unbalanced release of cytokines that drive lymphopenia including NK cell death and T cells depletion (160).