CD4 and major depressive disorder: Genome-wide association studies and epigenetic analysis revealed that genetic variants associated with depression were significantly enriched in epigenetic active sites of activated CD4+T lymphocytes, which may affect immune cell function, promote the increase of peripheral blood inflammatory markers (CRP, IL-1β, TNF-α, IL-6, IL-17) and increase leukocyte count, suggesting that the immune system may participate in the pathogenesis of MDD through inflammatory response (Lynall et al., 2022).