CD8A and infection: In summary, the severe disease outcome associated with intranasal, but not intratracheal, infection correlated with an enhanced innate immune response, indicated by elevated circulating neutrophils, and a robust adaptive immune response, marked by increased effector CD8 + cytotoxic T cells, accompanied by reduced eosinophils, pDCs, Tregs, and B cells (Fig. 4 and Online resource 4).