Medicine
Role of neutrophil extracellular traps in sepsis immunopathology
Quick fact
In sepsis, neutrophils cast nets of DNA and antimicrobial proteins that can clog microscopic blood vessels, contribute to organ failure, and even trigger clot formation—sometimes at the cost of the very patient they're meant to protect.
Why this is interesting
Your body's own defenders—neutrophils—release sticky webs that help trap invaders, but in sepsis these same webs become part of the problem. Imagine a fire brigade that sprays water but also floods the building.
Read the full explanation
Understanding Role of neutrophil extracellular traps in sepsis immunopathology
Neutrophils are front-line white blood cells that ingest and kill bacteria. When they meet a threat too large to swallow, they can explode—releasing a web of DNA, histones, and enzymes called a neutrophil extracellular trap, or NET. In a healthy infection, NETs physically trap and neutralize bacteria, preventing their spread. But in sepsis—a systemic, dysregulated response to infection—this process goes into overdrive. Massive NET formation occurs throughout the bloodstream, creating a condition known as a 'cytokine storm' where immune signals become chaotic. Instead of staying local, these webs spread everywhere, clogging fine capillaries, causing inflammation, and damaging the body's own tissues. So the same defense mechanism that works in a wart or a lung infection becomes a pathological agent when generalized.
A deeper explanation
The formation of NETs, termed NETosis, is triggered by bacteria, fungi, or inflammatory cytokines. It involves activation of the enzyme PAD4, which citrullinates histones—modifying their positive charge and causing chromatin to decondense. The nuclear envelope and cell membrane rupture, releasing a mesh of DNA studded with histones, elastase, and myeloperoxidase. While these are effective at trapping and killing microbes, in sepsis the effects are amplified and destructive. The DNA and histones are directly toxic to endothelial cells, the cells lining blood vessels, leading to vascular leakage. NETs also activate platelets and the clotting cascade, promoting microvascular thrombosis (disseminated intravascular coagulation, DIC). This combination of vascular damage and thrombi impairs blood flow to organs, contributing to multiple organ dysfunction syndrome. The immune system's attempt to contain a severe infection therefore inadvertently triggers a cascade of tissue injury. Understanding this mechanism points to potential therapies, such as DNase to degrade NETs or inhibitors of PAD4, but so far success in clinical trials has been limited, underscoring the complexity and dual nature of the immune response.