The DNA fibers of shrimp hemocyte extracellular traps are essential for the clearance of Escherichia coli.

Extracellular traps (ETs) are a part of the vertebrate immune response that was only recently discovered. These structures are formed in response to pathogenic invasion and they act to kill the invader. Vertebrate ETs are composed of chromosomal DNA, histone proteins and other antimicrobial cytoplasmic proteins. Pathogenic stimulation was also recently shown to trigger a similar ET response in shrimp hemocytes, and in the present study, we evaluate the role of the DNA fibers in the bactericidal properties of these invertebrate ETs. When the formation of shrimp ETs was disrupted by DNase I, the ETs anti-bacterial activity was also reduced, indicating that the DNA fibers are important for ET-mediated bacterial clearance. We also found that at high bacterial densities, shrimp ETs were a more effective anti-bacterial response than phagocytosis.

Shrimp hemocytes release extracellular traps that kill bacteria.

Extracellular traps (ETs) are formed from the DNA, histones and cytoplasmic antimicrobial proteins that are released from a range of vertebrate immune-cells in response to pathogenic stimulation. This novel defense mechanism has not been demonstrated in invertebrates. In this study, we investigated the formation of ETs in the crustacean Litopenaeus vannamei. We found that stimulation of shrimp hemocytes with phorbol myristate acetate (PMA), lipopolysaccharide (LPS) and live Escherichia coli all led to the formation of the characteristic ET fibers made from host cell DNA. After E. coli stimulation, we found that histone proteins were co-localized with these extracellular DNA fibers. The results further showed that E. coli were trapped by these ET-like fibers and that some of the trapped bacteria were permeabilized. All of these results are characteristic of the ETs that are seen in vertebrates and we therefore conclude that shrimp are also capable of forming extracellular traps.