There is now evidence that major depression is accompanied by significant changes in cell-mediated and humoral immunity, and these changes may be related to the pathophysiology or pathogenesis of that illness (Connor and Leonard [1], Dantzer et al. [2], Kim et al. [3], Licinio and Wong [4]), yet data are inconsistent. Some studies have shown that major depression is associated with dysregulation of immune mediators.
However, conflicting results have also been described (Brambilla and Maggioni [12], Brambilla et al. [13], Carpenter et al. [14], Rothermundt et al. [15]). These changes have been considered in terms of the imbalance between individual pro- and anti-inflammatory cytokines and the T helper 1 (Th1) and T helper 1 (Th2) imbalance in major depression. On the other hand, an enhanced secretion of such proinflammatory cytokines would not only lead to activation of T and B lymphocytes, but also could affect the brain and elicit various symptoms of depression, such as loss of appetite, listlessness, and sleep disturbances (Maes [16]).