As a response to various inflammatory stimuli, neutrophils and macrophages expel a mixture of their nuclear and granular elements in the form of extracellular traps (ETs). These web-like substances represent an evolutionarily conserved defense mechanism across humans, animals and even plants. ETs are composed of DNA, histones, and granular enzymes, and are capable of the entrapment of invading pathogens. Besides their protective function, ETs have been detected in a variety of pathological scenarios (from infections and autoimmune conditions to thrombosis) with detrimental effects, therefore they have been often referred to as ‘double-edged swords of immunity’. Most recently, neutrophil ETs have been identified as major contributors to the widespread immune-thrombosis in COVID-19 induced acute respiratory distress syndrome.
1. Understand the basic types of ETs and the route of their formation
2. Name three pathological conditions where ETs play a role
3. Outline the suspected steps of ET contribution to (COVID-19 triggered) thrombosis