Submitted on February 13, 2009
Accepted on March 4, 2009
Mechanisms of human complement factor B induction in sepsis and inhibition by activated protein C 
Kim Goring1, Yong Huang1, Connie Mowat1, Caroline Leger1, Teik-How Lim1, Raza Zaheer1, Dereck Mok1, Lee Anne Tibbles1, David Zygun1, and Brent Winston1*
1 University of Calgary
* To whom correspondence should be addressed. E-mail: bwinston{at}ucalgary.ca.
To investigate the potential role of the local expression of alternative complement factor B (hBf) in human sepsis, we examined the induction of Bf gene expression in human peripheral blood monocytes (PBMCs) from patients with septic shock and the mechanisms of hBf gene regulation by TNF
, IFN
and LPS in human monocytes. PBMCs from septic shock patients showed increased hBf mRNA expression compared to control patients. Co-stimulation with TNF and IFN, or stimulation with LPS, demonstrated a time- and dose-dependent induction of hBf mRNA expression in human PBMCs. A region of the hBf promoter between -735 and +128 bp was found to mediate IFN-, TNF- and LPS-responsiveness as well as the synergistic effect of IFN/TNF on hBf promoter activity. Site-directed mutagenesis of a GAS cis element (-90 to -82 bp) abrogated IFN-responsiveness. Mutagenesis of a NF-
B cis element at -466 to -456 bp abrogated TNF- and LPS-responsiveness of the Bf-promoter. Thus, hBf gene expression is induced in PBMCs from septic shock patients and the induction of hBf by IFN, TNF and LPS is through GAS and NF-B cis-binding sites on the hBf promoter. Further, activated protein C (APC) inhibited LPS-stimulated hBf promoter activity and protein expression in human monocytes suggesting that the beneficial effect of APC therapy in sepsis may in part be due to inhibition of complement induction and/or activation via the alternative pathway.
