Abstract
Depression has been increasingly associated with immune system dysregulation. This study investigates the potential of CD3 Gamma Subunit of T-Cell Receptor Complex (CD3G) as a diagnostic marker for depression, while also examining its role across various cancer types. Comparative analyses of immune cell infiltration and pathway activities were conducted using single-sample Gene Set Enrichment Analysis (ssGSEA) on datasets GSE98793. Depression patients were defined based on clinical diagnoses and compared to healthy controls (HC) without any psychiatric disorders. Differentially expressed genes (DEGs) were identified, followed by weighted gene co-expression network analysis (WGCNA), least absolute shrinkage and selection operator (LASSO) and logistic regression to pinpoint independent diagnostic markers. Functional enrichment analyses were performed to explore the biological implications of CD3G expression in depression. Pan-cancer analyses were also conducted to investigate CD3G's role in cancer. Depression patients exhibited significant decreases in CD8 T cells, cytotoxic cells, T cells, T helper cells, Tgd, and Th2 cells, with increased levels of dendritic cells and neutrophils compared to HC. Immune pathway activities showed increased antimicrobial, chemokine, cytokine, and TNF family member activities, with decreased TCR signaling activity in depression patients. CD3G was identified as a key immune-related gene and independent diagnostic marker for depression, validated by GSE76826 dataset. Low CD3G expression in depression was associated with enhanced immune response and inflammatory pathways. In pan-cancer analysis, CD3G was upregulated in numerous cancers and correlated with immune cell infiltration and oncogenic pathways. The study highlights significant dysregulation in immune cell infiltration and pathway activities in depression, with CD3G emerging as a critical immune-related gene and potential diagnostic marker. CD3G's role in immune modulation and cancer underscores its relevance in both depression and oncology, suggesting potential therapeutic targets and prognostic indicators.