IFITM (interferon-induced transmembrane protein) A small family of host transmembrane proteins induced by interferons that function in the cell's vesicular compartment to restrain various steps in viral replication.
IFN-α, IFN-β Antiviral cytokines produced by a wide variety of cells in response to infection by a virus, and which also help healthy cells resist viral infection. They act through the same receptor, which signals through a Janus-family tyrosine kinase. Also known as the type I interferons.
IFN-γ A cytokine of the interferon structural family produced by effector CD4 TH1 cells, CD8 T cells, and NK cells. Its primary function is the activation of macrophages, and it acts through a different receptor from that of the type I interferons.
IFN-γ-induced lysosomal thiol reductase (GILT) An enzyme present in the endosomal compartment of many antigen-presenting cells that denatures disulfide bonds to facilitate the degradation and processing of proteins.
IFN-λ Also called type III interferons, this family includes IL-28A, IL-28B, and IL-29, which bind a common receptor expressed by a limited set of epithelial tissues.
IFN-λ receptor Receptor composed of a unique IL-28Rα subunit and the β subunit of the IL-10 receptor that recognizes IL-28A, IL-28B, and IL-29.
Igα, Igβ See B-cell receptor.
IgA Immunoglobulin class composed of α heavy chains that can occur in a monomeric and a polymeric (mainly dimeric) form. Polymeric IgA is the main antibody secreted by mucosal lymphoid tissues.
IgA deficiency The class of immunoglobulin characterized by α heavy chains. It is the most common type of immunodeficiency. It can occur in a monomeric and a polymeric (mainly dimeric) form. Polymeric IgA is the main antibody secreted by mucosal lymphoid tissues.
IgD Immunoglobulin class composed of δ heavy chains that appears as surface immunoglobulin on mature B cells.
IgE Immunoglobulin class composed of ε heavy chains that acts in defense against parasite infections and in allergic reactions.
IgG Immunoglobulin class composed of γ heavy chains that is the most abundant class of immunoglobulin in the plasma.
IgM Immunoglobulin class composed of μ heavy chains that is the first to appear on B cells and the first to be secreted.
IgNAR See immunoglobulin new antigen receptor.
IgW Type of heavy-chain isotype present in cartilaginous fishes composed of six immunoglobulin domains.
IKK The IkB kinase, IKK, is a multisubunit protein complex composed of IKKα, IKKβ, and IKKγ (or NEMO).
IKKε A kinase that interacts with TBK1 (TANK-binding kinase 1) in the phosphorylation of IRF3 downstream of TLR-3 signaling.
IL-1 family   One of four major families of cytokines, this family contains 11 cytokines that are structurally similar to IL-1α, and are largely pro-inﬂammatory in function.
IL-1β A cytokine produced by active macrophages that has many effects in the immune response, including the activation of vascular endothelium, activation of lymphocytes, and the induction of fever.
IL-6   Interleukin-6, a cytokine produced by activated macrophages and which has many effects, including lymphocyte activation, the stimulation of antibody production, and the induction of fever.
IL-7 receptor (IL-7Rα) See CD127.