In our influenza hemagglutinin (HA) antigen-specific mouse model17–22, wild-type mice received adoptive transfer of 2.5 × 106 naïve HA-specific 6.5 CD4+ T cells from 6.5 donor mice (WT mice + 6.5 cells) and got 2.5 × 103 plaque-forming units (p.f.u.)PR8 strain of H1N1 influenza virus infection. Here, CD4 is linked to influenza.