MMP9 and infection: In addition, neutrophils are activated to undergo NETosis, which release the strands of decondensed DNA in complex with histones and a variety of proteolytic enzymes such as neutrophil elastase (NE), collagenase, and metal matrix proteases (MMP-9), known as neutrophil extracellular traps (NETs) [3], that can capture and kill bacteria and prevent the spread of infection.