Increase of NK–T cells in aged depressed patients not treated with antidepressive drugs

Background: A change in number and/or activity of natural killer cells has repeatedly been reported in depressive illness. Much less attention has yet been given to the subgroup of natural killer cells that are positive for the T-cell marker CD3 (NK–T cells). These cells possibly have important immunoregulatory properties. Methods: We compared number and percentage of NK–T cells (defined as CD3+ and CD16+ and/or CD56+ by two-color flow cytometry) in the peripheral blood of control subjects and two groups of elderly depressive subjects using or not using antidepressive drugs. Results: The number and percentage of NK–T cells were strongly elevated in elderly depressive subjects not using antidepressive drugs, as compared with control subjects and elderly depressive subjects using antidepressive drugs. Conclusions: Depressive illness in a geriatric population is associated with a substantial increase of NK–T cells. This increase was absent in a depressive group using antidepressive drugs