Despite larger titers of viruses recovered from the lung, infection with viruses expressing shutoff active NS1 (Cal[NS1_high-PAX_low] or Cal[NS1_high-PAX_high]) resulted in significantly fewer IAV-specific CD4+ and CD8+ T cells in the MLN and spleen at 7 dpi (Figure 1B and Figure 4A). Here, CD4 is linked to infection.