CD4 and infection: Although it was initially thought that CD4+ T cell help is not required for the generation of CD8+ T cell primary responses against infections due to the ability of infections to provide inflammatory signals for full activation of DCs to bypass the CD4+ T cell help, it is now clear that certain infections, such as vaccinia virus, influenza virus, adenovirus, also require CD4+ T cell help for CD8+ T cell priming [35]–[37].