(ii) Immune and inflammatory responses: during stress injury, the number of peripheral blood immune cells (CD4+ T cells, CD8+ T cells) is increased in PTSD patients, and the secretion of inflammatory cytokines (IL-2, IL-6, IL-8, tumor necrosis factor) in serum is abnormal (Bonne et al., 2011; O'Donovan et al., 2013). This evidence concerns the gene CD4 and post-traumatic stress disorder.