TNF and post-traumatic stress disorder: The initial evidence for the relationship between PTSD and the immune system comes from individual studies and subsequent meta-analyses reporting alterations in peripheral inflammatory markers, such as C-reactive protein (CRP), interferon-gamma (IFN-γ), interleukin-6 (IL-6), interleukin-10 (IL-10), and tumor necrosis factor-alpha (TNF-α) in individuals with PTSD (Fig. 1) [10, 20–23].