• Dan Li, Lin Zou, Yan Feng, Ganqiong Xu, Yu Gong, Gaofeng Zhao, Wen Ouyang, Joshua M Thurman, and Wei Chao.
• 1Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA. 2Department of Anesthesia, the Third Xiangya Hospital, Xiangya School of Medicine, Changsha, China. 3Department of Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA. 4Department of Medicine, University of Colorado School of Medicine, Aurora, CO.
• Crit. Care Med. 2016 May 1; 44 (5): e289-99.

ObjectivesToll-like receptors and complement are two components of the innate immunity. Complement factor B is essential for the alternative pathway of complement activation. We have recently reported that complement factor B is significantly up-regulated in the kidney and may contribute to acute tubular injury in an animal model of sepsis. This study investigates the mechanisms responsible for the complement factor B up-regulation and its role in sodium transporter expression in tubular cells during sepsis.DesignAnimal study.SettingLaboratory investigation.SubjectsC57BL/6 J wild-type, complement factor B(-/-), and Nfkb1(tm1Bal) p50(-/-) mice.InterventionsHuman proximal tubular cells and mouse tubular epithelial cells were stimulated with Toll-like receptor agonists. Bay 11-7082 was used to block nuclear factor-κB pathway. Alternative pathway activation was detected by C3 zymosan deposition. Polymicrobial sepsis was created by cecal ligation and puncture. Sodium transporter gene expression was determined by quantitative reverse transcriptase-polymerase chain reaction.Measurements And Main ResultsThe agonists for Toll-like receptor 4 (lipopolysaccharide) or Toll-like receptor 3 (polyinosinic-polycytidylic acid) induced a marked increase in complement factor B expression in human proximal tubular cells and mouse tubular epithelial cells both at gene and protein levels. The Toll-like receptor 1/2 agonist, Pam3cys, induced complement factor B production only in human proximal tubular cells, not in mouse tubular epithelial cells. The Toll-like receptor 9 ligand, CpG oligodeoxynucleotides failed to induce complement factor B production either in human proximal tubular cells or in mouse tubular epithelial cells. Lipopolysaccharide/polyinosinic-polycytidylic acid-induced complement factor B up-regulation was blocked by Bay 11-7082, a potent inhibitor of nuclear factor-κB signaling, and in mouse tubular epithelial cells deficient in p50 subunit of nuclear factor-κB. Media from the lipopolysaccharide-treated mouse tubular epithelial cell cultures contained de novo synthesized complement factor B and led to functional alternative pathway activation. In a cecal ligation and puncture model, wild-type septic mice had down-regulated expression of sodium transporters in the kidney compared with the sham. In comparison, complement factor B mice or mice treated with anti-complement factor B displayed preserved levels of Na⁺/K⁺ ATPase-α1 following sepsis.Conclusions1) Toll-like receptor 3/4 activation is sufficient to induce complement factor B production via nuclear factor-κB pathway and to enhance alternative pathway activation in the kidney tubular epithelial cells. 2) Complement factor B may contribute to the down-regulation of certain sodium transporter expression during sepsis.

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