CD8A and influenza: As a result of the homology of these internal proteins and highly conserved epitopes across the different subtypes (A/H1N1 and A/H3N2), the CD8+ T-cell response to influenza is cross-reactive among all of the strains of influenza A. Activation of T-cells leads to their migration to the infection site where they recognize influenza virus-infected cells and eliminate them via lytic activity.