Prior to PR8-HA-GP61-80 infection, we analyzed lung-infiltrating CD4+ T cells for cytokine expression following ex vivo gp61-80 peptide restimulation and found that primary LCMV i.n. infection induced significantly more IFNγ- and TNFα-producing T cells in the lung compared to adjuvanted rGP immunization at 39 dpi (S6D–S6E Fig) similar to our data of CD4+ T cells in the lymph nodes and spleen. Here, CD4 is linked to infection.