Absolute Number and Percentage of Circulating Natural Killer, Non-MHC-Restricted T Cytotoxic, and Phagocytic Cells in Unipolar Depression

One of the most consistently reported immunological abnormalities in major depression is blunted ex vivo natural killer cell activity (NKCA). This study was designed to investigate the number and percentage of circulating natural killer cells (NKC) in a group of patients with unipolar depression. In addition, the number and percentage of other phagocytic/cytotoxic cells were determined. The following cell subsets were investigated: number of leukocytes, monocytes, neutrophils, lymphocytes, NKC (CD 16+ or CD56+), and non-MHC-restricted cytotoxic T lymphocytes (CTL) in 17 healthy controls and 79 depressed subjects. There were no differences either in absolute number or percentage of NKC, or CTL between healthy controls, minor, simple major, and melancholic depressed subjects. Depression per se was characterized by a leukocytosis due to monocytosis and neutrophilia. Our results do not support the thesis that depression-related blunted NKCA is caused by a decreased number or percentage of NKC in peripheral blood.