Aged MPC CD4 T cells also had much higher expression of genes downstream of type I interferon (IFN) signaling, such as Stat1 and Irf7. Interestingly, we recently demonstrated that type I IFN signaling is a key signature of chronic viral infections compared to acute viral infections in both CD4 T cells41 and CD8 T cells42. Here, CD4 is linked to viral infectious disease.