Sections

Key Terms

Key Terms

adaptive immunity: immunity that has memory and occurs after exposure to an antigen either from a pathogen or a vaccination

affinity: attraction of molecular complementarity between antigen and antibody molecules

allergy: immune reaction that results from immediate hypersensitivities in which an antibody-mediated immune response occurs within minutes of exposure to a harmless antigen

antibody: protein that is produced by plasma cells after stimulation by an antigen; also known as an immunoglobulin

antigen: foreign or non-self protein that triggers the immune response

antigen-presenting cell (APC): immune cell that detects, engulfs, and informs the adaptive immune response about an infection by presenting the processed antigen on the cell surface

autoantibody: antibody that incorrectly marks self components as foreign and stimulates the immune response

autoimmune response: inappropriate immune response to host cells or self-antigens

autoimmunity: type of hypersensitivity to self antigens

avidity: total binding strength of a multivalent antibody with antigen

B cell: lymphocyte that matures in the bone marrow and differentiates into antibody-secreting plasma cells

basophil: leukocyte that releases chemicals usually involved in the inflammatory response

cell-mediated immune response: adaptive immune response that is carried out by T cells

clonal selection: activation of B cells corresponding to one specific BCR variant and the dramatic proliferation of that variant

complement system: array of approximately 20 soluble proteins of the innate immune system that enhance phagocytosis, bore holes in pathogens, and recruit lymphocytes; enhances the adaptive response when antibodies are produced

cross reactivity: binding of an antibody to an epitope corresponding to an antigen that is different from the one the antibody was raised against

cytokine: chemical messenger that regulates cell differentiation, proliferation, gene expression, and cell trafficking to effect immune responses

cytotoxic T lymphocyte (CTL): adaptive immune cell that directly kills infected cells via perforin and granzymes, and releases cytokines to enhance the immune response

dendritic cell: immune cell that processes antigen material and presents it on the surface of other cells to induce an immune response

effector cell: lymphocyte that has differentiated, such as a B cell, plasma cell, or cytotoxic T lymphocyte

eosinophil: leukocyte that responds to parasites and is involved in the allergic response

epitope: small component of an antigen that is specifically recognized by antibodies, B cells, and T cells; the antigenic determinant

granzyme: protease that enters target cells through perforin and induces apoptosis in the target cells; used by NK cells and killer T cells

helper T lymphocyte (T_H): cell of the adaptive immune system that binds APCs via MHC II molecules and stimulates B cells or secretes cytokines to initiate the immune response

host: an organism that is invaded by a pathogen or parasite

humoral immune response: adaptive immune response that is controlled by activated B cells and antibodies

hypersensitivities: spectrum of maladaptive immune responses toward harmless foreign particles or self antigens; occurs after tissue sensitization and includes immediate-type (allergy), delayed-type, and autoimmunity

immune tolerance: acquired ability to prevent an unnecessary or harmful immune response to a detected foreign body known not to cause disease or to self-antigens

immunodeficiency: failure, insufficiency, or delay at any level of the immune system, which may be acquired or inherited

inflammation: localized redness, swelling, heat, and pain that results from the movement of leukocytes and fluid through opened capillaries to a site of infection

innate immunity: immunity that occurs naturally because of genetic factors or physiology, and is not induced by infection or vaccination

interferon: cytokine that inhibits viral replication and modulates the immune response

lymph: watery fluid that bathes tissues and organs with protective white blood cells and does not contain erythrocytes

lymphocyte: leukocyte that is histologically identifiable by its large nuclei; it is a small cell with very little cytoplasm

macrophage: large phagocytic cell that engulfs foreign particles and pathogens

major histocompatibility class (MHC) I/II molecule: protein found on the surface of all nucleated cells (I) or specifically on antigen-presenting cells (II) that signals to immune cells whether the cell is healthy/normal or is infected/cancerous; it provides the appropriate template into which antigens can be loaded for recognition by lymphocytes

mast cell: leukocyte that produces inflammatory molecules, such as histamine, in response to large pathogens and allergens

memory cell: antigen-specific B or T lymphocyte that does not differentiate into effector cells during the primary immune response but that can immediately become an effector cell upon re-exposure to the same pathogen

monocyte: type of white blood cell that circulates in the blood and lymph and differentiates into macrophages after it moves into infected tissue

mucosa-associated lymphoid tissue (MALT): collection of lymphatic tissue that combines with epithelial tissue lining the mucosa throughout the body

natural killer (NK) cell: lymphocyte that can kill cells infected with viruses or tumor cells

neutrophil: phagocytic leukocyte that engulfs and digests pathogens

opsonization: process that enhances phagocytosis using proteins to indicate the presence of a pathogen to phagocytic cells

passive immunity: transfer of antibodies from one individual to another to provide temporary protection against pathogens

pathogen: an agent, usually a microorganism, that causes disease in the organisms that they invade

pathogen-associated molecular pattern (PAMP): carbohydrate, polypeptide, and nucleic acid “signature” that is expressed by viruses, bacteria, and parasites but differs from molecules on host cells

pattern recognition receptor (PRR): molecule on macrophages and dendritic cells that binds molecular signatures of pathogens and promotes pathogen engulfment and destruction

perforin: destructive protein that creates a pore in the target cell; used by NK cells and killer T cells

plasma cell: immune cell that secrets antibodies; these cells arise from B cells that were stimulated by antigens

regulatory T (T_reg) cell: specialized lymphocyte that suppresses local inflammation and inhibits the secretion of cytokines, antibodies, and other stimulatory immune factors; involved in immune tolerance

T cell: lymphocyte that matures in the thymus gland; one of the main cells involved in the adaptive immune system