naive T cells   Lymphocytes that have never encountered their specific antigen and thus have never responded to it, as distinct from effector and memory lymphocytes.
nasal-associated lymphoid tissue (NALT) Organized lymphoid tissues found in the upper respiratory tract. In humans, NALT consists of Waldeyer’s ring, which includes the adenoids, palatine, and lingual tonsils, plus other similarly organized lymphoid tissue located around the pharynx. It is part of the mucosal immune system.
natalizumab Humanized antibody to α4 integrin used to treat Crohn's disease and multiple sclerosis. It blocks lymphocytes' adhesion to endothelium, impairing their migration into tissues.
natural antibodies Antibodies produced by the immune system in the apparent absence of any infection. They have a broad specificity for self and microbial antigens, can react with many pathogens, and can activate complement.
natural cytotoxicity receptors (NCRs) Activating receptors on NK cells that recognize infected cells and stimulate cell killing by the NK cell.
natural interferon-producing cells See plasmacytoid dendritic cells.
natural killer (NK) cell A type of ILC that is important in innate immunity to viruses and other intracellular pathogens, and in antibody-dependent cell-mediated cytotoxicity (ADCC). NK cells express activating and inhibitory receptors, but not the antigen-specific receptors of T or B cells.
necrosis The process of cell death that occurs in response to noxious stimuli, such as nutrient deprivation, physical injury, or infection. To be distinguished from apoptosis, in which the cell activates an internal, or intrinsic, program of death, such as occurs in immune cells as a result of deficiency of cell survival signals.
negative selection The process by which self-reactive thymocytes are deleted from the repertoire during T-cell development in the thymus. Autoreactive B cells undergo a similar process in bone marrow.
NEMO See IKK.
NEMO deficiency See X-linked hypohidrotic ectodermal dysplasia and immunodeficiency.
neoepitopes Type of tumor rejection antigen created by mutations in protein that can be presented by self-MHC molecules to T cells.
neonatal Fc receptor (FcRn) See FcRn.
neuraminidase An inﬂuenza virus protein that cleaves sialic acid from host cells to allow viral detachment, a common antigenic determinant, and target of antiviral neuraminidase inhibitors.
neutralization Inhibition of the infectivity of a virus or the toxicity of a toxin molecule by the binding of antibodies.
neutralizing antibodies Antibodies that inhibit the infectivity of a virus or the toxicity of a toxin.
neutropenia Abnormally low levels of neutrophils in the blood.
neutrophil The most numerous type of white blood cell in human peripheral blood. Neutrophils are phagocytic cells with a multilobed nucleus and granules that stain with neutral stains. They enter infected tissues and engulf and kill extracellular pathogens.
neutrophil elastase Proteolytic enzyme stored in the granules of neutrophils that is involved in the processing of antimicrobial peptides.
neutrophil extracellular traps (NETs) A meshwork of nuclear chromatin that is released into the extracellular space by neutrophils undergoing apoptosis at sites of infection, serving as a scaffold that traps extracellular bacteria to enhance their phagocytosis by other phagocytes.
NFκB A heterodimeric transcription factor activated by the stimulation of Toll-like receptors and also by antigen receptor signaling composed of p50 and p65 subunits.
NFAT See nuclear factor of activated T cells.