decay-accelerating factor (DAF or CD55) A cell-surface protein that protects cells from lysis by complement. Its absence causes the disease paroxysmal nocturnal hemoglobinuria.
Dectin-1 A phagocytic receptor on neutrophils and macrophages that recognizes β-1,3-linked glucans, which are common components of fungal cell walls.
defective ribosomal products (DRiPs) Peptides translated from introns in improperly spliced mRNAs, translations of frameshifts, or improperly folded proteins, which are recognized and tagged by ubiquitin for degradation by the proteasome.
defensins See α-defensins, β-defensins.
delayed-type hypersensitivity reactions A form of cell-mediated immunity elicited by antigen in the skin stimulating sensitized Th1 CD4 lymphocytes and CD8 lymphocytes. It is called delayed-type hypersensitivity because the reaction appears hours to days after antigen is injected. Referred to as type IV hypersensitivity in the historic Gell and Coombs classification.
dendritic cells   Bone marrow-derived cells found in most tissues, including lymphoid tissues. There are two main functional subsets. Conventional dendritic cells take up antigen in peripheral tissues, are activated by contact with pathogens, and travel to the peripheral lymphoid organs, where they are the most potent stimulators of T-cell responses. Plasmacytoid dendritic cells can also take up and present antigen, but their main function in an infection is to produce large amounts of the antiviral interferons as a result of pathogen recognition through receptors such as TLRs. Both these types of dendritic cells are distinct from the follicular dendritic cell that presents antigen to B cells in lymphoid follicles.
dendritic epidermal T cells (dETCs) A specialized class of γ:δ T cells found in the skin of mice and some other species, but not humans. They express Vγ5:Vδ1 and may interact with ligands such as Skint-1 expressed by keratinocytes.
dephosphorylation The removal of a phosphate group from a molecule, usually a protein.
depleting antibodies Immunosuppressive monoclonal antibodies that trigger the destruction of lymphocytes in vivo. They are used for treating episodes of acute graft rejection.
diacyl and triacyl lipoproteins   Ligands for the Toll-like receptors TLR1:TLR2 and TLR2:TLR6.
diacylglycerol A lipid intracellular signaling molecule formed from membrane inositol phospholipids that are cleaved by the action of phospholipase C-γ after the activation of many different receptors. The diacylglycerol stays in the membrane and activates protein kinase C and RasGRP, which further propagate the signal.
diapedesis The movement of blood cells, particularly leukocytes, from the blood across blood vessel walls into tissues.
differentiation antigens   Referring to a category of genes with restricted expression patterns that can be targeted as antigens by immunotherapies in treatment of cancers.
DiGeorge syndrome Recessive genetic immunodeficiency disease in which there is a failure to develop thymic epithelium. Parathyroid glands are also absent and there are anomalies in the large blood vessels.
direct allorecognition Host recognition of a grafted tissue that involves donor antigen-presenting cells leaving the graft, migrating via the lymph to regional lymph nodes, and activating host T cells bearing the corresponding T-cell receptors.
direct presentation The process by which proteins produced within a given cell give rise to peptides presented by MHC class I molecules. This may refer to antigen-presenting cells, such as dendritic cells, or to nonimmune cells that will become the targets of CTLs.