DEPRESSION, STRESS AND IMMUNOLOGICAL ACTIVATION - THE ROLE OF CYTOKINES IN DEPRESSIVE-DISORDERS

Traditionally, both stress and depression have been associated with im paired immune function and increased susceptibility to infectious and neoplastic disease. However over the last number of years a large body of evidence suggests that major depression is associated with signs o f immunological activation. Moreover it has been suggested that cytoki ne hypersecretion may be involved in the aetiology of depressive disor ders. The present article reviews the evidence from both clinical and experimental studies which implicates immunological activation and par ticularly hypersecretion of cytokines in the onset and maintenance of depressive illness. Both clinical and experimental studies indicate th at stress and depression are associated with increased circulating con centrations of cytokines such as IL-1 beta, IL-6 and gamma-IFN and pos itive acute phase proteins, and hyperactivity of the HPA-axis. In addi tion, it has been reported that immunological activation induces ''str ess-like'' behavioural and neurochemical changes in laboratory animals . Although for many years it has been suggested that stress acts a pre disposing factor to depressive illness, the precise mechanisms by whic h stress-induced depressive symptoms occur are not fully understood. N evertheless, behavioural changes due to stress have often been explain ed in terms of changes in neurotransmitter function in the brain. In t he present article increased cytokine secretion is implicated as a mec hanism whereby stress can induce depression.