ATF6 and post-traumatic stress disorder: In contrast, the Past PTSD > 5y group exhibits much stronger biomarker inter-correlations, with IL-18 showing high correlations with IRE1 (ρ = 0.879), pERK (ρ = 0.879), and ATF6 (ρ = 0.895), all significant (adjusted p = 0.006), reflecting a tightly coupled inflammatory and stress response in chronic PTSD.