The enrichment scores of activated dendritic cells, macrophages, monocytes, natural killer cells, and regulator T cells in MDD patients were significantly higher than those in healthy controls, while the scores of activated B cell, activated CD8+ T cell, effector memory CD8+ T cell, memory B cell, and type 1 T helper cell were lower (all Ps < 0.05, Figure 6B). Here, CD8A is linked to major depressive disorder.