TNF and post-traumatic stress disorder: Furthermore, peripheral blood mononuclear cells (PBMCs) isolated from post-traumatic stress disorder (PTSD) patients have elevated spontaneous pro-inflammatory cytokine expression, e.g., interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α), providing evidence that PBMCs can be a circulating biological indicator or biomarker of neuroinflammation after injury [18].