The following is a summary of the “Plasma complement C3 and C3a are increased in major depressive disorder independent of childhood trauma” published in the November 2022 issue of Psychiatry by Luo et al.

The pathophysiology of serious depression may be related to a dysfunctional complement system (MDD). In addition, the incidence of depression in later life has been linked to exposure to trauma in childhood, possibly due to immunological activation. The purpose of this study was to examine the association between adult Post-traumatic stress disorder and peripheral levels of complement C3, C3a, C1q, and C-reactive protein (CRP) in patients with MDD and healthy controls.

About 49 people with MDD who were not taking medication and 45 who were not sick served as participants. A childhood trauma questionnaire was given to all participants, and then blood was taken to analyze complement levels (C3, C3a, C1q, and CRP) using an enzyme-linked immunosorbent assay. Medication-free MDD patients had a larger concentration of C3 and C3 in their peripheral plasma than the healthy controls, whereas the depressed patients had a similar concentration of C1q and CRP to the healthy controls.

Patients diagnosed with MDD did not show any correlation between exposure to these inflammatory variables and a history of childhood trauma. Despite the lack of association between traumatic childhood experiences and circulating levels of complement C3, C3a, C1q, and CRP, our data suggest that complement C3 and C3 a may be involved in the pathophysiology of MDD.