Neuroendocrine-immunological abnormalities that are established during a stressful childhood are thought to mediate the development of the pro-inflammatory phenotype in adulthood [33], [34] including reduced cortisol awakening response [86]. This could result in altered expression of certain cytokine levels in plasma, since cortisol levels are known to regulate immune and inflammatory responses. For example, stress has been shown to promote the expression of certain cytokines [87], correlations were found between reduced cortisol and increased aggression in adolescents and young men [88]–[90], and maltreatment in childhood was shown to lead to low basal cortisol in association with conduct and aggressive disorders [91]. However, the associations between stress, cortisol, cytokines and aggression are complex since opposite results have also been reported. Indeed, glucocorticoids produced by the adrenal gland are strong immunosupressors known to directly repress the expression of many cytokines in leucocytes including the cytokines examined here. For example, a study of the males from the present study during adolescence, reported that high cortisol levels were associated with high levels of aggression [92]. Therefore, both hyper- and hypo-active stress responses have been shown to associate with aggression [93].
