A growing body of research suggests that inflammatory cytokines might have systemic effects in addition to their role in the immune response. Recent studies have shown that changes in cytokine expression levels are associated with various behavioral disorders such as anxiety, depression, suicide, childhood mood disorder and post-traumatic stress disorder (PTSD) [17]–[28]. In normal men, assessments of hostility, physical aggression, and verbal aggression were positively associated with lipopolysaccharide stimulated TNF-α expression in blood monocytes [29]. Moderate to severe maltreatment during childhood was also observed to be positively correlated with overall change in stress-induced IL-6 concentrations [30]. Other studies examined the association between cytokines and aggression in animals. Gene knockout depletion of IL-6 (−/−) in mice resulted in increased aggression compared to control mice and over-expression of IL-6 in the brain of normal mice increases affiliative behavior [31]. We have recently shown that consistent with these data in mice, physical aggression of boys during childhood is associated with reduced plasma levels of cytokines later in early adulthood [32]. Compared to the control group, men on a chronic physical aggression trajectory from
