Iron is one of the most important trace elements in the body, and its homeostasis is essential to the normal function of the immune system. Complement component C3, which is the converging of three main pathways of complement system activation, plays a key role in the innate immunity. However, the relationship between iron homeostasis and complement C3 remains unknown. The aim of our study was to analyze the relationship between serum iron and ferritin level and complement C3 and C4. A total of 590 healthy individuals were recruited in our study. Higher serum complement C3 level (p < 0.001) was found in individuals with higher serum ferritin level (> 104.0 μg/L). Moreover, serum iron level and serum ferritin level were positively correlated with complement C3 (r = 0.133, p = 0.001; r = 0.221, p < 0.001) and complement C4 (r = 0.117, p = 0.004; r = 0.123, p = 0.003). The linear regression analysis displayed that both serum iron level and serum ferritin level were linearly correlated with serum complement C3 level (adjusted beta: 2.382, 95% CI: 0.841–3.923; adjusted beta: 42.911, 95% CI: 29.070–56.751). To explore the relationship between iron homeostasis and complement C3 further, the serum samples from C3^−/− mice and the wild-type (WT) control mice were obtained. Significantly lower serum iron level and higher ferritin level were found in C3^−/− mice than those in WT mice (p < 0.001; p < 0.001), indicating that complement C3 might influence iron distribution and utilization. Overall, these data suggested that serum iron and ferritin levels were correlated with complement C3. The deficiency of complement C3 may disrupt the regular iron metabolism in the body.

铁是体内最重要的微量元素之一，其体内平衡对免疫系统的正常功能至关重要。补体成分 C3 是补体系统激活的三个主要途径的汇聚，在先天免疫中起着关键作用。然而，铁稳态和补体 C3 之间的关系仍然未知。我们研究的目的是分析血清铁和铁蛋白水平与补体 C3 和 C4 之间的关系。我们的研究共招募了 590 名健康个体。 在血清铁蛋白水平较高 (> 104.0 μg/L) 的个体中发现血清补体 C3 水平较高 ( p < 0.001)。此外，血清铁水平和血清铁蛋白水平与补体 C3 呈正相关（r  = 0.133，p  = 0.001；r  = 0.221, p  < 0.001) 和补 C4 ( r  = 0.117, p  = 0.004; r  = 0.123, p  = 0.003)。线性回归分析显示，血清铁水平和血清铁蛋白水平均与血清补体 C3 水平呈线性相关（调整β：2.382，95% CI：0.841–3.923；调整β：42.911，95% CI：29.070–56.751）。为了进一步探索铁稳态和补体 C3 之间的关系，获得了来自 C3 ^-/-小鼠和野生型 (WT) 对照小鼠的血清样品。在 C3 ^-/-小鼠中发现的血清铁水平和铁蛋白水平明显低于WT 小鼠（p  < 0.001；p  < 0.001)，表明补体 C3 可能影响铁的分布和利用。总之，这些数据表明血清铁和铁蛋白水平与补体 C3 相关。补体 C3 的缺乏可能会破坏体内正常的铁代谢。