Thus, during pulmonary infection, acute inflammation results in the migration of neutrophils out of capillaries and into the air spaces, forming a marginated pool of neutrophils that is ready to respond when needed. These neutrophils phagocytize microbes and kill them with reactive oxygen species, antimicrobial proteins, and degradative enzymes. They also extrude a chromatin meshwork containing antimicrobial proteins that trap and kill extracellular bacteria, known as neutrophil extracellular traps (NETs). Various membrane receptors and ligands are involved in the complex interaction between microbes, cells of the lung parenchyma, and immune defense cells.[14]