CD4 and infection: As one study found neither infection of the lung nor antigen persistence was required for establishment in the lung of antigen-specific CD8+ T cells [131], we found similar results in our study investigating CD4+ T cells as adjuvanted rGP immunization showed minimal lung-resident memory CD4+ T cells prior to influenza challenge but had significantly expanded secondary effector CD4+ T cells and CD4+ TRM in the lung compared to primary influenza infection, suggesting either increased trafficking to the lung or a larger antigen-specific memory TRM pool compared to naïve mice.