Natural killer cell activity in patients with major depressive disorder treated with escitalopram.

Background: An association between depression and altered immunity has been suggested by many studies, although the findings are not fully consistent. The present investigation examined the effects of escitalopram on cellular immunity in patients with major depressive disorder (MDD).

Methods: Fifty-one patients with MDD were evaluated with the Hamilton Rating Scale for Depression and Montgomery-Åsberg Depression Rating Scale. The patients were grouped into responders (n=32) and non-responders (n=19). Adrenocorticotropic hormone, cortisol, CD4, CD8, CD19, and natural killer cells were measured at baseline and after a 4 week treatment with escitalopram. Plasma hormones and immune parameters were compared between groups.

Results: Responders showed increased activity, but not number, of natural killer cells after a 4 week treatment with escitalopram. There were no differences in plasma hormones and other immune parameters between groups, even though cortisol was decreased and CD19 was increased across both groups compared to baseline.

Conclusions: The results suggest that natural killer cells play an important role in improving the symptoms of depressive patients responding to selective serotonin inhibitors. To deepen our understanding of the pathogenesis of depression, interactions between serotonin and the immune system should be further explored.