The complement system and the CD14/TLR4/MD2 complex as targets for therapy in sepsis.

This project aims to develop a new therapeutic regimen for conditions where the innate immune system is over-activated and induces disease, as seen in sepsis. We have previously shown that inhibition of key molecules of two important branches if innate immunity, the complement system and the TRL-system, to a great extent attenuate the inflammatory response induced by bacteria in vitro. In particular, combined inhibition of these systems has proven particularly effective. We have in this project characterized several inhibitors of central components in these systems. In particular, we have documented that a small molecule called coversin (OmCI) efficiently inhibits complement component C5 both in pigs and humans. We have used coversin in a porcine model of sepsis with beneficial effects both on inflammation and haemostasis. Furthermore, we have worked with antibodies to CD14, a key molecule in the TLR family. Combined inhibition of CD14 and C5 was found to be more efficient than single treatment in porcine sepsis. We have also produced recombinant anti-CD14 antibodies both to pig and human CD14, which is based on a IgG2/4 chimera lacking the adverse effects of the original antibodies. The results obtained so far in the project have led to 21 original publications in well acknowledged Journals (of which 6 in The Journal of Immunology). The last paper in the Thesis of the PhD candidate on this project revealed why previously studies on treatment of sepsis did not succeed by inhibiting innate immunity by a TLR4 specific inhibitor (published with the candidate as first author in Journal of Infectious Diseases.

The complement system and the Toll-like receptors are two main innate recognition systems initiating the host response to exogenous and endogenous molecular patterns leading to danger signalling. The response is characterized by an inflammatory reaction w ith a broad range of biological mediators expressed on cell surfaces or secreted from the cells. Complement is a protein cascade systems, which normally acts locally and under controlled conditions to prevent the host and to maintain tissue homeostasis. H owever, it is a double-edged sward in the sense that improper or excessive systemic activation, as seen in sepsis, may contribute to the breakdown of homeostatic mechanisms leading to a serious inflammatory response syndrome with multiple organ failure an d irreversible septic shock. Novel agents blocking complement activation has reduce the inflammatory reaction and improved survival in animal models of sepsis, but clinical studies are missing. Activation of the Toll-like receptor system potently induces a number of inflammatory reactions, with the LPS-recognition CD14/TRL4/MD-2 complex as a an essential actor in sepsis induced by Gram-negative bacteria. We have recently shown that a combined inhibition of complement and CD14 virtually abolish all inflamm atory mediators induced by Gram-negative bacteria in a human whole blood model of sepsis. Thus, we hypothesize that combined inhibition of these two essential upstream recognition systems might be an appropriate strategy for future therapy of sepsis. This hypotheses will be tested in vivo, using a pig model established in our laboratory, and in mouse and baboon sepsis models established in the groups of our international collaborators.