IFIT2 and infection: Together, these results suggest that the IFIT2 reporter correlates more with the measure of infection–induced viral stress (or associated viral fitness) than activation of an immune-protected or non-permissive cell state; evolved reduced-fitness N1 strains (Figure 4) activate a reduced stress response (Figure 2A), while evolved higher-fitness N4 strains (Figure 2A) activate a more elevated stress response (Figure 4).