PTSD is associated with neuroimmune suppression: evidence from PET imaging and postmortem transcriptomic studies

Area of Science:

• Neuroscience
• Psychiatry
• Immunology

Background:

• Peripheral immune activation is recognized in posttraumatic stress disorder (PTSD).
• Limited research exists on brain immune regulation in individuals with PTSD.
• Prevailing hypotheses suggest neuroinflammation is central to stress-related disorders.

Purpose of the Study:

• To investigate brain immunologic regulation in individuals with PTSD.
• To examine the relationship between microglial activation, peripheral inflammation, and PTSD symptom severity.
• To challenge existing neuroimmune activation theories in PTSD.

Main Methods:

• Utilized [11C]PBR28 Positron Emission Tomography (PET) brain imaging to assess 18-kDa translocator protein (TSPO) availability, a marker for microglial activity.
• Recruited 23 individuals with PTSD and 26 healthy controls (with or without trauma exposure).
• Analyzed C-reactive protein (CRP) levels and gene expression in postmortem brain tissue from PTSD patients and controls.

Main Results:

• Lower TSPO availability in the prefrontal-limbic regions of the brain was observed in the PTSD group compared to controls.
• Reduced TSPO availability was negatively associated with PTSD symptom severity.
• Higher C-reactive protein levels correlated with lower prefrontal-limbic TSPO availability and increased PTSD severity.
• Postmortem analysis revealed lower relative expression of TSPO and microglia-associated genes (TNFRSF14, TSPOAP1) in a subgroup of female PTSD patients.

Conclusions:

• Findings suggest a potential deficit in brain microglial activation in PTSD, despite peripheral immune activation.
• This challenges the prevailing hypothesis that widespread neuroinflammation is a core mechanism in PTSD pathophysiology.
• The study highlights the complex interplay between peripheral and central immune responses in PTSD.