The Immune System

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Pathogen Noun

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[path-uh-jen]

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Pathogen

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A biological agent, such as a virus, bacterium, or fungus, that causes disease or illness to its host.

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Example: A pathogen is a disease-causing agent, which can be cellular (living) like bacteria and fungi, or acellular (non-living) like viruses and prions.

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Antigen Noun

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[an-ti-jen]

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Antigen

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A substance, often a protein on a pathogen's surface, that triggers an immune response and the production of antibodies.

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Example: This image shows that an antigen is a specific marker on the surface of a pathogen, which a matching antibody can recognize and bind to.

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Antibody Noun

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[an-ti-bod-ee]

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Antibody

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A Y-shaped protein produced by B cells that identifies and neutralizes foreign objects like bacteria and viruses.

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Example: This diagram shows a Y-shaped antibody with a specific antigen-binding site that perfectly fits a corresponding antigen, illustrating its role in targeting invaders.

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Phagocytosis Noun

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[fag-uh-sy-toh-sis]

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Phagocytosis

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The process by which certain living cells, called phagocytes, ingest or engulf other cells or particles like bacteria.

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Example: This diagram shows a cell's plasma membrane wrapping around and engulfing a large particle, like a bacterium, to form an internal pouch called a vacuole.

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Inflammation Noun

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[in-fluh-mey-shun]

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Inflammation

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A localized defensive response to tissue injury, characterized by redness, heat, swelling, and pain, to limit pathogen spread.

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Example: This image shows six common signs of inflammation, such as redness, swelling, and pain, which are the body's response to injury or infection.

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Pyrexia Noun

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[py-rek-see-uh]

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Pyrexia

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An abnormal elevation of body temperature, commonly known as a fever, that is often a response to infection.

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Example: A person's body temperature is being measured with a thermometer, which is used to detect pyrexia (fever), a common sign of an immune response.

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B cell Noun

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[bee sel]

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B cell

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A type of lymphocyte, a white blood cell, that is responsible for producing and secreting antibodies in the immune system.

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Example: A B cell recognizes a specific antigen, becomes activated, and interacts with a helper T cell to help initiate a targeted immune response.

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T cell Noun

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[tee sel]

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T cell

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A type of lymphocyte, a white blood cell, that plays a central role in cell-mediated immunity.

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Example: This diagram shows how an immature T cell is activated by an antigen and then matures into either a helper T cell or a cytotoxic T cell.

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Memory cell Noun

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[mem-uh-ree sel]

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Memory cell

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A long-lived lymphocyte capable of responding to a particular antigen on its reintroduction, long after the initial exposure.

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Example: This diagram shows how after a first infection (Primary Response), memory B cells are created and 'remember' the invader for a faster, stronger future defense (Secondary Response).

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Immunity Noun

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[ih-myoo-ni-tee]

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Immunity

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The ability of an organism to resist a particular infection or toxin by the action of specific antibodies or white blood cells.

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Example: This diagram shows several types of specialized white blood cells, such as macrophages and neutrophils, that are part of the body's innate immunity.