KEY TERMS

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

adaptiveimmunity

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-presentingcell(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

antigen

a macromolecule that reacts with cells of the immune system and which may or may not have a stimulatory effect

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-mediatedimmuneresponse

an adaptive immune response that is controlled by T cells

complementsystem

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

cytotoxicTlymphocyte(TC)

an adaptive immune cell that directly kills infected cells via enzymes, and that releases cytokines to enhance the immune response

dendriticcell

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

helperTlymphocyte(TH)

a cell of the adaptive immune system that binds APCs via MHC class II olecules and stimulates B cells or secretes cytokines to initiate the mmune response

humoralimmuneresponse

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

immunetolerance

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

innateimmunity

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

majorhistocompatibilityclass (MHC) IImolecule

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

majorhistocompatibilityclass (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

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

naturalkiller(NK) cell

a lymphocyte that can kill cells infected with viruses or tumor cells

neutrophil

a phagocytic leukocyte that engulfs and digests pathogens

passiveimmunity

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

primaryimmuneresponse

the response of the adaptive immune system to the first exposure to an antigen

secondaryimmuneresponse

the response of the adaptive immune system to a second or later exposure to an antigen mediated by memory cells

Tcell

a lymphocyte that matures in the thymus gland

vaccine

a weakened solution of virus components, viruses, or other agents that produce an immune response

viralenvelope

a lipid bilayer that envelops some viruses

virion

an individual virus particle outside a host cell

whitebloodcell

a nucleated cell found in the blood that is a part of the immune system; also called leukocytes