C3 and depressive disorder: Research has also associated other pro-inflammatory biomarkers with mental health disorders and complement component 3 (C3), interleukin 6 (IL-6), leptin and white blood cell count (WBC) concentrations are reported to be higher in subjects with depression (Cernea et al., 2019; Luo et al., 2022; Shafiee et al., 2017; Ting et al., 2020).