As expected, CD8+ T cell-mediated cytolysis was markedly enhanced by SF-10 in the early phase of IAV infection (Fig 4), and effects of CD8+ and CD4+ depletion in mice immunized with HAv-SF-10 showed that CD4+ T cells predominantly while CD8+ T cells partially contributed to mice survival in the advanced stage of severe pneumonia (Fig 5). Here, CD4 is linked to susceptibility to pneumonia measurement.