Innate immunity, the first line of immune defense, uses a system of host pattern recognition receptors (PRRs) to recognize signals of “danger” including invariant pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). These signals in turn recruit and assemble protein complexes called inflammasomes, resulting in the activation of caspase-1, the processing and release of the pro-inflammatory cytokines IL-1ß and IL-18, and the induction of programmed, lytic cell death known as pyroptosis.
Innate immunity and the activity of the inflammasome are critical for successful immunity against a myriad of environmental pathogens. However dysregulation of inflammasome activity is associated with many inflammatory diseases including type 2 diabetes, obesity-induced asthma, and insulin resistance. Recently, aberrant NLRP3 inflammasome activity also has been associated with age-related macular degeneration and Alzheimer disease. Understanding the players and regulators involved in inflammasome activity and regulation may provide additional therapeutic targets for these diseases.
The ability to isolate and assay circulating cell-free DNA from plasma holds promise for improved diagnostics and treatment in the clinic. The use of blood-based non-invasive prenatal testing (NIPT) has been well described. Such testing is based on circulating cell-free fetal DNA in blood of a pregnant woman for diagnosis and screening of chromosomal anueploidy (e.g. Trisomy 21, Down Syndrome), sex-linked diseases, and genetic diseases that are known to result from a specific mutation in a single gene (1). Additionally, most cancers carry somatic mutations that are unique to the tumors, and dying tumor cells release small pieces of their DNA into the blood stream (2). This circulating cell-free tumor DNA can be used as a biomarker to “follow” cancer progression or regression during treatment, and diagnostic methods also are being developed to detect even early stage cancers from circulating tumor DNA (3). Further, increases in circulating cell-free DNA have been well documented after intense exercise, trauma, sepsis and even associated with autoimmune diseases such as system lupus erythematosus (SLE; 1,4). In these latter examples increases in extracellular DNA are associated with evolutionarily conserved innate immune responses involving the production of neutrophil extracellular traps (NETs). Monitoring the circulating cell-free DNA of NETs has implications for treatment and diagnosis of autoimmune diseases, cardiovascular events and traumatic injuries (4–7).
How Neutrophils Weave a Defensive Web
Neutrophils are the most abundant type of white blood cell and are part of the innate immune response, participating in non-specific immune responses to injury or pathogens. They are one of three types of granuolcytes, and can be recognized by their multi-lobed nucleus and the prominent granules that fill their cytoplasm. Generally they are first to the scene of injury or infection. Early in my scientific career, I was taught that neutrophils fought disease via phagocytosis and occasionally by firing a barrage of toxic enzymes and molecules at invaders. Mostly though they released cytokines that recruited the “important” cells of the specific immune system to the area.
For these reasons, I never really thought much about neutrophils. That is until recently, when I learned about Neutrophil Extracellular Traps (NETs). It turns out that neutrophils are pretty awesome, sacrificing themselves in a cloud-like explosion of DNA, chromatin, and granule proteins Continue reading “Weaving Tangled Webs with Cell-Free DNA”