The tissue damage seen in sepsis — which is triggered most often by a microbial infection and can cause organ failure and death — is caused by a component of red blood cells. Help is at hand, however, as the blood also contains a protein that combats these effects.

Bacterial infection causes red blood cells to rupture, releasing the oxygen-transporting molecule haemoglobin. As this oxidizes, it releases free haeme, which can trigger programmed cell death. Miguel Soares at the Gulbenkian Institute of Science in Oeiras, Portugal, and his team found that mice lacking a protein that breaks down haeme had higher levels of haeme in their blood and an increased susceptibility to sepsis. In addition, administering extra haeme to normal mice pushed low-grade infections to become septic. But giving the animals a protein called haemopexin neutralized haeme's toxic effects.

Sci. Transl. Med. 2, 51ra71 (2010)