Granulocyte Colony-Stimulating Factor Worsens the Outcome of Experimental <em>Klebsiella pneumoniae</em> Pneumonia Through Direct Interaction With the Bacteria

Besides its well-established effects on granulocytopoiesis, granulocyte colony-stimulating factor (G-CSF) has been shown to have direct effects on the recruitment and bactericidal ability of neutrophils, resulting in improved survival of experimentally infected animals. We studied the effect of G-CSF on the course of experimental pneumonia induced by an important gram-negative bacillary pulmonary pathogen. Using a highly reproducible murine model, we here show the paradoxical finding that mortality from infection was significantly increased when animals received G-CSF before induction of pneumonia. Administration of G-CSF promoted replication of bacteria in the liver and spleen, thus indicating an impairment rather than an enhancement of antibacterial mechanisms. By contrast, a monoclonal antibody against K2 capsule significantly reduced bacterial multiplication in the lung, liver, and spleen, and abrogated the increased mortality caused by G-CSF. In vitro studies showed a direct effect of G-CSF on resulting in increased capsular polysaccharide (CPS) production. When bacteria were coincubated with therapeutically achievable concentrations of G-CSF, phagocytic uptake and killing by neutrophils was impaired. Western blot analysis showed three binding sites of G-CSF to Binding of125I-G-CSF to was displaced by an excess of unlabeled G-CSF, whereas an unrelated cytokine, interleukin-1α, did not compete with G-CSF binding to the bacteria. Thus, in this model, the direct effect of G-CSF on a bacterial virulence factor, CPS production, outweighed any beneficial effect of G-CSF on recruitment and stimulation of leukocytes.

除了对粒细胞生成已确立的作用外，粒细胞集落刺激因子（G - CSF）已被证明对中性粒细胞的募集和杀菌能力有直接影响，从而提高了实验感染动物的存活率。我们研究了G - CSF对一种重要的革兰氏阴性杆菌性肺部病原体所诱发的实验性肺炎病程的影响。利用一种高度可重复性的小鼠模型，我们在此呈现了一个矛盾的发现：当动物在诱发肺炎前接受G - CSF时，感染所致的死亡率显著增加。给予G - CSF促进了细菌在肝脏和脾脏中的繁殖，这表明抗菌机制受到了损害而非增强。相比之下，一种针对K2荚膜的单克隆抗体显著减少了细菌在肺、肝脏和脾脏中的繁殖，并消除了由G - CSF导致的死亡率增加。体外研究表明，G - CSF对导致荚膜多糖（CPS）产生增加有直接影响。当细菌与治疗可达到浓度的G - CSF共同孵育时，中性粒细胞的吞噬摄取和杀伤能力受损。蛋白质印迹分析显示G - CSF有三个结合位点。过量未标记的G - CSF可置换¹²⁵I - G - CSF与的结合，而一种无关的细胞因子白细胞介素 - 1α并不与G - CSF和细菌的结合竞争。因此，在该模型中，G - CSF对一种细菌毒力因子——CPS产生的直接影响，超过了G - CSF对白细胞募集和刺激的任何有益作用。