The complement system is a vital component of the innate immune system, though its role in bacteremia is poorly understood. We present complement levels in Staphylococcus aureus bacteremia (SAB) and Gram-negative bacteremia (GNB) and describe observed associations of complement levels with clinical outcomes. Complement and cytokine levels were measured in serum samples from 20 hospitalized patients with SAB, 20 hospitalized patients with GNB, 10 non-infected hospitalized patients, and 10 community controls. C5a levels were significantly higher in patients with SAB as compared to patients with GNB. Low C4 and C3 levels were associated with septic shock and 30-day mortality in patients with GNB, and elevated C3 was associated with a desirable outcome defined as absence of (1) septic shock, (2) acute renal failure, and (3) death within 30 days of bacteremia. Low levels of C9 were associated with septic shock in patients with GNB but not SAB. Elevated IL-10 was associated with increased 30-day mortality in patients with SAB. Complement profiles differ in patients with SAB and those with GNB. Measurement of IL-10 in patients with SAB and of C4, C3, and C9 in patients with GNB may help to identify those at higher risk for poor outcomes.

补体系统是先天免疫系统的重要组成部分，尽管它在菌血症中的作用还鲜为人知。我们介绍金黄色葡萄球菌中的补体水平菌血症（SAB）和革兰氏阴性菌血症（GNB），并描述了观察到的补体水平与临床结局的关联。在20例SAB住院患者，20例GNB住院患者，10例未感染住院患者和10例社区对照的血清样本中测量了补体和细胞因子水平。SAB患者的C5a水平明显高于GNB患者。低水平的C4和C3水平与败血症患者的败血性休克和30天死亡率相关，而升高的C3与理想的结局相关，定义为不存在（1）败血性休克，（2）急性肾衰竭和（3）细菌血症30天内死亡。低水平的C9与GNB患者而非败血症患者的败血性休克有关。IL-10升高与SAB患者30天死亡率增加有关。SAB患者和GNB患者的补体谱不同。SAB患者中IL-10的测定以及GNB患者C4，C3和C9的测定可能有助于确定那些不良预后较高的患者。