Serum Levels of IFN-γ and NGF as Potential Biomarkers of Depressive Disorders

Background: Depressive disorder (DD) is a widespread mental illness that lacks objective diagnostic biomarkers, complicating early detection and personalized treatment. This study investigated the diagnostic value of serum interferon-gamma (IFN-γ), nerve growth factor (NGF), and their ratio, alongside thyroid peroxidase antibody (TPOAb) and glial fibrillary acidic protein (GFAP), in patients with DD compared to healthy controls. Methods: A total of 238 participants (118 with DD and 120 controls) were enrolled. Depression severity was assessed using DSM-5 and HAM-D criteria. Serum biomarkers were measured using enzyme-linked immunosorbent assays (ELISA), and receiver operating characteristic (ROC) analysis was performed to assess diagnostic performance. Results: DD patients exhibited significantly lower IFN-γ and higher NGF levels than controls (both p < 0.001), resulting in a markedly reduced IFN-γ/NGF ratio. The IFN-γ/NGF ratio achieved the highest diagnostic accuracy (AUC = 0.858, sensitivity = 82.20%, specificity = 77.50%), outperforming IFN-γ (AUC = 0.766) and NGF (AUC = 0.848) alone. TPOAb and GFAP levels did not differ significantly between groups. Conclusion: The IFN-γ/NGF ratio is a promising biomarker for depressive disorder, offering superior diagnostic accuracy over individual immune or neurotrophic markers. This composite index may support more objective and biologically informed diagnosis in clinical psychiatry.