CD4 and major depressive disorder: described twelve populations upregulated in MDD patients, compared to healthy controls: these include total leukocyte, granulocyte, basophil, neutrophil and monocyte absolute counts, but also more specific subsets such as natural killer (NK) cells, B cells, intermediate monocytes, both naïve and memory CD4+ Th cells, immature double positive T cells and CD25+ and HLA-DR+ activated T cells.