IL4 and post-traumatic stress disorder: For studies investigating inflammation in PTSD according to peripheral inflammatory markers, the current review identified and selected 24 studies that explored serum levels of proinflammatory cytokines including one or more of IL-1β, IL-6, TNF-α, and IFN-γ as well as CRP, and 19 studies that explored serum levels of anti-inflammatory cytokines IL-4 and/or IL-10.