Plasma complement component 4 increases in patients with major depressive disorder.

Elevation of plasma inflammatory factors in major depressive disorder (MDD) has been repeatedly observed, but contradictory results have also been reported. Alteration of complement components in MDD may also contribute to the pathophysiology of MDD by participating in inflammation. The recent findings that complement component 4 (C4) was involved in neural synapse elimination and associated with schizophrenia implicated the potential roles of C4 in MDD. In this study, we analyzed the plasma concentration of complement C4 and inflammatory factors, including interleukin (IL)-1β, IL-6, IL-8, IL-10, interferon-α, interferon-γ and tumor necrosis factor-α, of 53 patients with MDD and 60 healthy individuals. The plasma of 17 patients out of 51 after antidepressant medication was also collected for analysis. The results showed that peripheral C4 in MDD was higher than that in healthy controls. No significant correlation of inflammatory factors or C4 with depressive or anxiety symptoms was found. Antidepressant medication significantly reduced plasma C4 of patients with MDD. Our results were consistent with previous findings that complement components were elevated in MDD and suggested that C4 might play a role in pathophysiology of MDD and could be a candidate in the research of biomarker and the pathophysiology of MDD.