C4BP runs damage control

The complement inhibitor C4b-binding protein (C4BP) prevents necrotic cells from spilling their pro-inflammatory guts, according to a study on page 1937. Trouw and colleagues now show that C4BP and its binding partner, anticoagulant protein S (PS), cooperate to grab onto necrotic cells and to inhibit the release of cellular DNA.

C4BP short-circuits the complement cascade by binding to the activated complement components C3b and C4b and presenting them to the proteolytic complement inhibitor Factor I for degradation. This inhibitory capacity of C4BP can be coopted by bacterial pathogens, which coat themselves with this protein to avoid complement-mediated destruction by phagocytic cells.

This group recently identified a role for the C4BP–PS complex: it binds to apoptotic cells through the phosphatidylserine-binding domain of PS. This association could prevent...