Pyroptosis

Pyroptosis is a highly inflammatory form of lytic programmed cell death that occurs most frequently upon infection with intracellular pathogens and is likely to form part of the antimicrobial response. This process promotes the rapid clearance of various bacterial, viral, fungal and protozoan infections by removing intracellular replication niches and enhancing the host's defensive responses. Pyroptosis can take place in immune cells and is also reported to occur in keratinocytes and some epithelial cells. The process is initiated by formation of a large supramolecular complex termed the inflammasome (also known as a pyroptosome) upon intracellular danger signals. The inflammasome activates a different set of caspases as compared to apoptosis, for example, caspase-1/4/5 in humans and caspase-11 in mice. These caspases contribute to the maturation and activation of the pro-inflammatory cytokines IL-1β and IL-18, as well as the pore-forming protein gasdermin D. Formation of pores causes cell membrane rupture and release of cytokines, as well as various damage-associated molecular pattern (DAMP) molecules such as HMGB-1, ATP and DNA, out of the cell. These molecules recruit more immune cells and further perpetuate the inflammatory cascade in the tissue. However, in pathogenic chronic diseases, the inflammatory response does not eradicate the primary stimulus. A chronic form of inflammation ensues that ultimately contributes to tissue damage. Pyroptosis is associated with diseases including autoinflammatory, metabolic, and cardiovascular diseases, as well as cancer and neurodegeneration. Some examples of pyroptosis include the cell death induced in Salmonella-infected macrophages and abortively HIV-infected T helper cells. This type of inherently pro-inflammatory programmed cell death was named pyroptosis in 2001 by Molly Brennan and Dr. Brad T. Cookson, an associate professor of microbiology and laboratory medicine at the University of Washington. The Greek pyro refers to fire and ptosis means falling.