A growing body of work suggests that individuals with aggressive behavior and/or aggressive tendencies have evidence of chronic, low level, inflammation as manifested by elevated circulating levels of acute phase reactant proteins and pro-inflammatory cytokines. While animal studies report that direct application of pro-inflammatory proteins in brain increase aggressive behavior, there is no data on the relationship of central levels of these proteins and aggression in human subjects. We simultaneously measured levels of both plasma and lumbar cerebrospinal fluid (CSF) C-Reactive Protein (CRP) and IL-6, IL-8, and TNF-α in 77 medically healthy, drug-free, individuals with varying degrees of aggression including 22 individuals with DSM-5 Intermittent Explosive Disorder (IED). Aggression was assessed using the Life History of Aggression (LHA) and the Buss-Perry Aggression Questionnaire (BPAQ). Plasma and CSF levels of CRP, IL-8, and TNF-α, but not IL-6, correlated significantly with each other. Aggressive individuals with IED displayed elevated plasma, but not CSF, levels of proinflammatory markers and this relationship was specific to IED. Similarly, composite aggression scores correlated significantly with plasma, but not CSF, pro-inflammatory markers. Aggressive behavior in humans is correlated with Plasma, but not CSF, proinflammatory markers despite the observation that these two sets of markers are significantly correlated. Since the direct application of proinflammatory proteins in brains of animals increase aggressive behavior, proinflammatory proteins likely influence brain-based behavior in a manner not reflected in lumbar CSF.

Intermittent Explosive Disorder (IED) is a disorder of impulsive aggression affecting 4-7% of the U.S. population during some period of life. In addition to other biological correlates, elevations of plasma inflammatory markers have been reported in IED, compared with control, subjects. In this study we sought to explore if treatment exposure to anti-aggressive agents, compared with placebo, would be associated with a reduction in circulating levels of inflammatory markers. Thirty IED subjects, from a 12-week, double-blind, randomized, placebo-controlled trial of fluoxetine and divalproex, in which both pre- and post-treatment levels of C-Reactive Protein (CRP), interleukin (IL)-1β, IL-2, IL-6, IL-8, IL-10 and tumor necrosis factor (TNF)-α were obtained. Efficacy measures included the Overt Aggression Scale-Modified (OAS-M) score for Aggression and for Irritability, rate of Clinical Global Impression of Improvement (CGI-I), and rate of IED Remitters at study completion. As compared to placebo, neither fluoxetine nor divalproex reduced any of the measures of aggression. In addition, levels of CRP and pro- and anti-inflammatory cytokines showed no changes from pre- to post-treatment for any treatment condition. Correlations between pre- and post- treatment plasma CRP/cytokines were substantial (mean r=0.71, r(2)=0.50, p<0.001). Overall, circulating markers of inflammation markers were unaffected by treatment with fluoxetine or divalproex, consistent with the absence of change in measures of impulsive aggression.