In the present study, we explored the association between complement C4 levels and SZ and found that the complement C4 level in serum was lower among patients with SZ than among healthy controls. In addition, this study also demonstrated that the complement C4 level in the serum of male patients with SZ was lower than that in healthy controls, and similar results were observed in females. Our results indicate that abnormalities in C4 level are associated with the emergence of SZ in both males and females. Our finding of significantly reduced C4 levels in patients with SZ compared to healthy controls duplicates the discovery of Mayilyan et al. (2008), which suggested a similar outcome. In contrast, Maes et al. (1997) reported that C4 levels were significantly higher in patients with SZ. In the Maes et al. (1997) study, all cases were of the chronic or subchronic type, and they were all free of psychiatric illnesses or long-term chronic disease and the use of drugs that interfere with immune function, which may account for the inconsistency with our findings. Additionally, previous studies (Fernandes et al., 2010; Santos Sória et al., 2012) showed that there was no significant difference in the serum level of C4 between patients with SZ and healthy controls; however, an increased level of C3 was observed for cases, which may indicate that the activation of the complement system occurred through an alternative pathway. In addition, there are many other factors (Sopeña et al., 1996; Aral et al., 2006; El-Fatah Fahmy Hanno et al., 2014; Wakabayashi et al., 2016) that may influence the level of C4, such as a history of using drugs and suffering from other diseases, smoking and drinking habits and so on.
The complement system mediates innate and acquired immunity, and the activation of the complement component can remove damaged cells and autoantigens (Nimgaonkar et al., 2017). However, the mechanisms of how C4 affects SZ merit further investigation. Kopczynska et al. (2017) reported that select complement analyte measurements could be used to aid in the early diagnosis of SZ. The results of our study also suggest that serum C4 levels may be associated with SZ. Therefore, C4 has the potential to become a biomarker for the diagnosis and efficacy evaluation of SZ and other mental disorders.
This study was supported by the Innovation and Entrepreneurship Training Program Fund of Jilin University.
There are no conflicts of interest.
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