inflammation   General term for the local accumulation of ﬂuid, plasma proteins, and white blood cells that is initiated by physical injury, infection, or a local immune response.
inflammatory bowel disease (IBD) General name for a set of inﬂammatory conditions in the gut, such as Crohn’s disease and colitis, that have an immunological component.
inflammatory cells   Cells such as macrophages, neutrophils, and effector TH1 lymphocytes that invade inﬂamed tissues and contribute to the inﬂammation.
inflammatory chemokines Chemokines that are produced in response to infection or injury to direct the localization of immune cells to sites of inﬂammation.
inflammatory inducers Chemical structures that indicate the presence of invading microbes or cellular damage, such as bacterial lipopolysaccharides, extracellular ATP, or urate crystals.
inflammatory mediators Chemicals such as cytokines produced by immune cells that act on target cells to promote defense against microbes.
inflammatory monocytes An activated form of monocyte producing a variety of pro-inﬂammatory cytokines.
inflammatory response See inflammation.
infliximab   Chimeric antibody to TNF-α used in the treatment of inﬂammatory diseases, such as Crohn's disease and rheumatoid arthritis.
inherited immunodeficiency diseases See primary immunodeficiencies.
inhibitory receptors   On NK cells, receptors whose stimulation results in suppression of the cell’s cytotoxic activity.
initiator caspases Proteases that promote apoptosis by cleaving and activating other caspases.
iNKT See invariant NKT cells.
innate immunity The various innate resistance mechanisms that are encountered first by a pathogen, before adaptive immunity is induced, such as anatomical barriers, antimicrobial peptides, the complement system, and macrophages and neutrophils carrying nonspecific pathogen-recognition receptors. Innate immunity is present in all individuals at all times, does not increase with repeated exposure to a given pathogen, and discriminates between groups of similar pathogens, rather than responding to a particular pathogen. Cf. adaptive immunity.
innate lymphoid cells (ILCs) See ILCs.
innate recognition receptors General term for a large group of proteins that recognize many different inﬂammatory inducers and that are encoded in the germline and do not need gene rearrangement in somatic cells to be expressed.
inositol 1,4,5-trisphosphate (IP3) A soluble second messenger produced by the cleavage of membrane inositol phospholipids by phospholipase C-γ. It acts on receptors in the endoplasmic reticulum membrane, resulting in the release of stored Ca2+ into the cytosol.
integrin Heterodimeric cell-surface proteins involved in cell–cell and cell–matrix interactions. They are important in adhesive interactions between lymphocytes and antigen-presenting cells and in lymphocyte and leukocyte adherence to blood vessel walls and migration into tissues.
integrin α4:β7   Integrin binding to VCAM-1, MAdCAM-1, and fibronectin and expressed by various cells, such as IELs, that traffic to intestinal lamina propria.
intercellular adhesion molecules (ICAMs) See ICAMs.
interdigitating dendritic cells See dendritic cells.
interferon regulatory factor (IRF) A family of nine transcription factors that regulate a variety of immune responses. For example, IRF3 and IRF7 are activated as a result of signaling from some TLRs. Several IRFs promote expression of the genes for type I interferons.