While CD4+ T cell help (TH) is
critical for inducing optimal B cell and CD8+ T cell responses, it
remains unclear whether induction of CD4+ TH responses after
infection, are also dependent on CD4+ T cell help. Here we show that activation of adoptively
transferred TH cells during primary influenza A virus (IAV)
infection enhances both the magnitude and functional breadth of endogenous primary
IAV-specific CD4+ T cell responses. This enhancement was dependent
on CD154-CD40 dependent DC licensing and resulted in a greater recall capacity of
IAV-specific CD4+ and CD8+ T memory responses after heterologous
IAV infection. These data suggest that engaging pre-existing CD4 responses at
the time of priming maybe a strategy for improving cellular immunity after
vaccination.