IL4R and infection: To evaluate whether down-regulation of cell surface IL-4Rα expression on activated CD8+ T cells is specific to VV infections, we analyzed IL-4Rα expression on effector (GzmB+ CD62L−) and naïve (GzmB− CD62L+) CD8+ T cells as described in Yuen et al[23] following infection of BALB/c WT mice with VV-WR, modified vaccinia Ankara (MVA), avirulent Semliki Forest virus (aSFV), fowlpox virus (FPV) or A/PR8 (H1N1) influenza virus (figure 4A).