BDNF and influenza: Indeed, influenza vaccine has been shown to lead to the recruitment of T lymphocytes from the periphery to the choroid plexus in mice, which promote increased levels of brain-derived growth factor (BDNF) and insulin-like growth factor-1 (IGF-1) in the hippocampus in communication with resident cells, whereas these effects were abolished by anti-TCR antibody treatment (Qi et al., 2016).