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acellular
lacking cells
active immunity
an immunity that occurs as a result of the activity of the body’s own cells rather than from antibodies acquired from an external source
adaptive immunity
a specific immune response that occurs after exposure to an antigen either from a pathogen or a vaccination
allergy
an immune reaction that results from immediate hypersensitivities in which an antibody-mediated immune response occurs within minutes of exposure to a harmless antigen
antibody
a protein that is produced by plasma cells after stimulation by an antigen; also known as an immunoglobulin
antigen
a macromolecule that reacts with cells of the immune system and which may or may not have a stimulatory effect
antigen-presenting cell (APC)
an immune cell that detects, engulfs, and informs the adaptive immune response about an infection by presenting the processed antigen on its cell surface
apoptosis
the cell death caused by induction of a cell’s own internal mechanisms either as a natural step in the development of a multicellular organism or by other environmental factors such as signals from cells of the immune system
attenuation
the weakening of a virus during vaccine development
autoantibody
an antibody that incorrectly marks “self” components as foreign and stimulates the immune response
autoimmunity
a type of hypersensitivity to self-antigens
B cell
a lymphocyte that matures in the bone marrow
capsid
the protein coating of the viral core
cell-mediated immune response
an adaptive immune response that is controlled by T cells
complement system
an array of approximately 20 soluble proteins of the innate immune system that enhance phagocytosis, bore holes in pathogens, and recruit lymphocytes
cytokine
a chemical messenger that regulates cell differentiation, proliferation, and gene expression to effect immune responses
cytopathic
causing cell damage
cytotoxic T lymphocyte (TC)
an adaptive immune cell that directly kills infected cells via enzymes, and that releases cytokines to enhance the immune response
dendritic cell
an immune cell that processes antigen material and presents it on the surface of its cell in MHC class II molecules and induces an immune response in other cells
effector cell
a lymphocyte that has differentiated, such as a B cell, plasma cell, or cytotoxic T cell
glycoprotein
a protein molecule with attached carbohydrate molecules
helper T lymphocyte (TH)
a cell of the adaptive immune system that binds APCs via MHC class II molecules and stimulates B cells or secretes cytokines to initiate the immune response
humoral immune response
the adaptive immune response that is controlled by activated B cells and antibodies
hypersensitivity
a spectrum of inappropriate immune responses toward harmless foreign particles or self-antigens; occurs after tissue sensitization and includes immediate-type (allergy), delayed-type, and autoimmunity
immune tolerance
an acquired ability to prevent an unnecessary or harmful immune response to a detected foreign body known not to cause disease
immunodeficiency
a failure, insufficiency, or delay at any level of the immune system, which may be acquired or inherited
inflammation
the localized redness, swelling, heat, and pain that results from the movement of leukocytes through opened capillaries to a site of infection
innate immunity
an immunity that occurs naturally because of genetic factors or physiology, and is not caused by infection or vaccination
interferon
a cytokine that inhibits viral replication
lymph
the watery fluid present in the lymphatic circulatory system that bathes tissues and organs with protective white blood cells and does not contain erythrocytes
lymphocyte
a type of white blood cell that includes natural killer cells of the innate immune system and B and T cells of the adaptive immune system
macrophage
a large phagocytic cell that engulfs foreign particles and pathogens
major histocompatibility complex (MHC) I
a group of proteins found on the surface of all nucleated cells that signals to immune cells whether the cell is normal or is infected or cancerous; it also provides the appropriate sites into which antigens can be loaded for recognition by lymphocytes
major histocompatibility complex (MHC) II molecule
a protein found on the surface of antigen-presenting cells that signals to immune cells whether the cell is normal or is infected or cancerous; it provides the appropriate template into which antigens can be loaded for recognition by lymphocytes
mast cell
a leukocyte that produces inflammatory molecules, such as histamine, in response to large pathogens
memory cell
an antigen-specific B or T lymphocyte that does not differentiate into an effector cell during the primary immune response but that can immediately become an effector cell on reexposure to the same pathogen
monocyte
a type of white blood cell that circulates in the blood and lymph and differentiates into a macrophage after it moves into infected tissue
natural killer (NK) cell
a lymphocyte that can kill cells infected with viruses or tumor cells
neutrophil
a phagocytic leukocyte that engulfs and digests pathogens
passive immunity
an immunity that does not result from the activity of the body’s own immune cells but by transfer of antibodies from one individual to another
primary immune response
the response of the adaptive immune system to the first exposure to an antigen
secondary immune response
the response of the adaptive immune system to a second or later exposure to an antigen mediated by memory cells
T cell
a lymphocyte that matures in the thymus gland
vaccine
a weakened solution of virus components, viruses, or other agents that produce an immune response
viral envelope
a lipid bilayer that envelops some viruses
virion
an individual virus particle outside a host cell
white blood cell
a nucleated cell found in the blood that is a part of the immune system; also called leukocytes
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