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Background TLR4 signaling mediates early inflammation after cold I/R. We hypothesized that the TLR4 co-receptor CD14, the intracellular adaptor proteins MyD88 and TRIF would be required for cold I/R induced inflammation. HMGB1 is a putative endogenous activator of TLR4. Therefore, we also assessed the contribution of HMGB1 in cold I/R induced inflammation. Methods Syngeneic heart transplants were performed in mice deficient in CD14, MyD88, TRIF, or wild-type mice. In other experiments, anti-HMGB1 neutralizing antibody or control IgG was administered at reperfusion. Donor hearts were subjected to 2 hours of cold ischemia and retrieved after 3 hours of reperfusion. Results After cold I/R, grafts revealed striking translocation of HMGB1 out of the nucleus in cardiac myocytes. Administration of an anti-HMGB1 neutralizing antibody resulted in reduced systemic IL-6 and TNFα and ICAM-1 mRNA levels (p≤0.05). Compared to controls, CD14KO mice exhibited significantly lower (p≤0.05) systemic IL-6 and JE/MCP-1 levels after cold I/R. Intra-graft TNFα and IL-1β mRNA levels were also significantly lower (p≤0.05) in CD14KO grafts. MyD88KO mice exhibited significantly lower (p≤0.05) systemic IL-6 levels compared to control mice after cold I/R. Intra-graft TNFα, IL-6, and ICAM1 mRNA levels were also significantly lower (p≤0.05) in MyD88KO grafts. Significantly lower levels (p≤0.05) of serum IL-6, MCP-1 as well as intragraft TNFα, IL-6, IL-1β, and ICAM1 were observed after cold I/R in TRIF deficient animals compared to controls. Conclusions CD14, MyD88, TRIF, and HMGB1 contribute to the inflammatory response that occurs after cold I/R. These results provide insight into the mechanisms of TLR4-mediated inflammation after cold I/R.

The systemic inflammatory response observed in the setting of overwhelming infection bears striking similarities to that observed in the setting of severe traumatic injury from a clinical and physiologic standpoint. Recent observations have demonstrated that these disparate clinical entities share common mediators on a molecular level. TLRs, specifically TLR4, and the endogenous molecule high-mobility group box 1 are among the mediators that are known to play a role in inflammation in the setting of sepsis. Evidence is accumulating that demonstrates that these mediators also play a role in the host response to tissue injury. Here, we highlight findings from the 7th World Conference on Trauma, Shock, Inflammation and Sepsis in Munich, Germany, in the context of this growing body of literature.

We report orthotopic (life‐supporting) survival of genetically engineered porcine cardiac xenografts (with six gene modifications) for almost 9 months in baboon recipients. This work builds on our previously reported heterotopic cardiac xenograft (three gene modifications) survival up to 945 days with an anti‐CD40 monoclonal antibody‐based immunosuppression. In this current study, life‐supporting xenografts containing multiple human complement regulatory, thromboregulatory, and anti‐inflammatory proteins, in addition to growth hormone receptor knockout (KO) and carbohydrate antigen KOs, were transplanted in the baboons. Selective “multi‐gene” xenografts demonstrate survival greater than 8 months without the requirement of adjunctive medications and without evidence of abnormal xenograft thickness or rejection. These data demonstrate that selective “multi‐gene” modifications improve cardiac xenograft survival significantly and may be foundational for paving the way to bridge transplantation in humans.