Chapter 35 | The Immune System – Key Vocabulary

Vocabulary flashcards summarizing all key immune-system terms from the lecture notes.

Pathogen

An organism or virus that causes disease.

Immune System

An animal body’s system of defenses against agents that cause disease.

Innate Immunity

A defense common to all animals that is active immediately upon exposure to pathogens and is the same whether or not the pathogen has been encountered previously.

Adaptive Immunity

A vertebrate-specific defense mediated by B and T lymphocytes that exhibits specificity, memory, and self–non-self recognition; also called acquired immunity.

Lysozyme

An enzyme that destroys bacterial cell walls; found in mammalian sweat, tears, and saliva.

Phagocytosis

Endocytosis in which large particles or microorganisms are taken up by a cell; performed by macrophages, neutrophils, and dendritic cells.

Toll-Like Receptor (TLR)

A membrane receptor on a phagocytic white blood cell that recognizes molecular fragments common to groups of pathogens.

Neutrophil

The most abundant white blood cell; phagocytic and self-destructs after destroying invaders.

Macrophage

A phagocytic cell that destroys microbes in innate immunity and serves as an antigen-presenting cell in adaptive immunity.

Natural Killer Cell

A white blood cell that kills tumor cells and virus-infected cells as part of innate immunity.

Cytokine

A small signaling protein secreted by various cells, including macrophages and helper T cells, that regulates the function of other cells.

Interferon

An antiviral or immune-regulatory protein; virus-infected cells secrete interferons that help nearby cells resist infection.

Complement System

About 30 blood proteins that amplify inflammation, enhance phagocytosis, or directly lyse extracellular pathogens.

Inflammatory Response

An innate defense triggered by injury or infection, causing swelling, recruitment of white blood cells, and tissue repair.

Histamine

A substance released by mast cells that dilates blood vessels and increases their permeability during inflammation and allergic responses.

Lymphocyte

A white blood cell that mediates immune responses; the main classes are B cells and T cells.

Thymus

A small organ in the thoracic cavity where T cells complete their maturation.

T Cells

Lymphocytes that mature in the thymus; include effector cells for cell-mediated immunity and helper cells for both branches of adaptive immunity.

B Cells

Lymphocytes that complete development in the bone marrow and become effector cells for the humoral immune response.

Antigen

A substance that elicits an immune response by binding to receptors of B cells, antibodies, or T cells.

Antigen Receptor

A surface protein on B or T cells that binds antigens and initiates adaptive immune responses.

Epitope

A small, accessible region of an antigen that is recognized by an antigen receptor or antibody; also called an antigenic determinant.

Antibody

A protein (immunoglobulin) secreted by plasma cells that binds a specific antigen; has a Y-shaped structure.

Immunoglobulin (Ig)

Another name for an antibody; a Y-shaped protein produced by plasma cells that binds specific antigens.

Major Histocompatibility Complex (MHC) Molecule

A host protein that displays peptide fragments for recognition by T cells; foreign MHC on transplants can trigger rejection.

Antigen Presentation

The process in which an MHC molecule binds an intracellular antigen fragment and displays it on the cell surface for T-cell recognition.

Effector Cell

A lymphocyte that has undergone clonal selection and can mediate an adaptive immune response.

Plasma Cell

An antibody-secreting effector cell of humoral immunity derived from activated B cells.

Memory Cell

A long-lived lymphocyte formed during the primary response that can mount a rapid secondary response on re-exposure to the antigen.

Clonal Selection

The process by which an antigen selects and activates lymphocytes with specific receptors, leading to proliferation of effector and memory clones.

Primary Immune Response

The initial adaptive response to an antigen, appearing after a lag of about 10–17 days.

Secondary Immune Response

A faster, stronger, and longer-lasting adaptive response elicited on subsequent exposures to the same antigen.

Humoral Immune Response

The adaptive-immunity branch that activates B cells and produces antibodies to defend against pathogens in body fluids.

Cell-Mediated Immune Response

The adaptive-immunity branch that activates cytotoxic T cells to defend against infected cells.

Helper T Cell

A T cell that secretes cytokines to promote responses of B cells and cytotoxic T cells to antigens.

Antigen-Presenting Cell

A cell (macrophage, dendritic cell, or B cell) that displays peptide-MHC complexes to T cells after ingesting pathogens.

Cytotoxic T Cell

An activated lymphocyte that kills infected cells, certain cancer cells, and transplanted cells.

Immunization

The artificial induction of immunity; includes active vaccination and passive administration of antibodies.

Monoclonal Antibodies

A uniform preparation of antibodies produced by a single clone of cultured cells, all specific for the same epitope.

Allergen

An antigen that provokes an exaggerated (allergic) immune response.

Autoimmune Disease

A disorder in which the immune system attacks the body's own cells and tissues.

Human Immunodeficiency Virus (HIV)

The retrovirus that causes AIDS by impairing the immune system.