Inflammasome

The inflammasome is a multiprotein oligomer consisting of caspase 1, PYCARD, NALP and sometimes caspase 5 (also known as caspase 11 or ICH-3). It is expressed in myeloid cells and is a component of the innate immune system. The exact composition of an inflammasome depends on the activator which initiates inflammasome assembly, e.g. dsRNA will trigger one inflammasome composition whereas asbestos will assemble a different variant. The inflammasome promotes the maturation of the inflammatory cytokines Interleukin 1β (IL-1β) and Interleukin 18 (IL-18).

The inflammasome is responsible for activation of inflammatory processes, and has been shown to induce cell pyroptosis, a process of programmed cell death distinct from apoptosis.

The inflammasome was discovered by the team of Prof. Jürg Tschopp, at the University of Lausanne, in 2002.

During an infection, one of the first forms of defense employed by the innate immune response is a group of pattern recognition receptors (PRRs) encoded in the germline to recognize molecular patterns expressed by invading pathogens. These may either be on the membrane surface e.g. Toll-like receptors (TLRs) and C-type Lectin Receptors (CLRs) or inside the cytoplasm e.g. Nod-like receptors (NLRs) and RIG-I-like receptors (RLRs). In 2002, it was first reported by Martinon et al. that a subset of NLRs named NLRP1 were able to assemble and oligomerize into a common structure which collectively activated the caspase-1 cascade, thereby leading to the production of pro-inflammatory cytokines especially IL-1B and IL-18. This NLRP1 multi-molecular complex was dubbed the ‘inflammasome’, which spurred much interest in the following years; since then, several other inflammasomes were discovered, two of which are also NLR subsets—NLRP3 and NLRC4. More recently, Hornung et al. classified an inflammasome of the PYHIN (pyrin and HIN domain-containing protein) family, termed absent in melanoma 2 (AIM2) which assembles upon sensing foreign cytoplasmic double-stranded DNA (dsDNA). Notably, the pyrin domain of the adaptor protein ASC has recently been shown to function as a prion-like domain, through a self-perpetuating manner upon activation.

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