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Chapter 12. Pathology and Psychology

Together with a series of physical barriers (the skin, mucous membranes, tears, and stomach acid), the immune system helps to defend the body against foreign or harmful substances that attempt to infiltrate it (Table 12-1). Such substances include microorganisms (bacteria, viruses, and fungi), parasites (such as worms), cancer cells, and even transplanted organs and tissues. Antigens are entities within or on bacteria, viruses, other microorganisms, or cancer cells that stimulate an immune response in the body. Antigens may also exist independently—eg, as pollen or food molecules. A normal immune response consists of the initial recognition of a foreign antigen, and the mobilization of forces to defend against it.

Table 12-1. Terms and Definitions of the Immune Systema
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Table 12-1. Terms and Definitions of the Immune Systema

TERM

DEFINITION

Antibody (immunoglobulin)

A protein that is produced by B lymphocytes and that interacts with a specific antigen

Antigen

Any substance that can stimulate an immune response

Baso phil

A white blood cell that releases histamine (a substance involved in allergic reactions) and produces substances to attract neutrophils and eosinophils to a trouble spot

Cell

The smallest unit of a living organism, composed of a nucleus and cytoplasm surrounded by a membrane

Chemotaxis

The process of attracting cells by means of a chemical substance

Complement system

A group of proteins with various immune functions, such as killing bacteria and other foreign cells, making foreign cells easier for macrophages to identify and ingest, attracting macrophages and neutrophils to a trouble spot, and enhancing the effectiveness of antibodies

Cytokines

The immune system's messengers, which help regulate an immune response

Dendritic cell

A white blood cell that usually resides in tissues and that helps T lymphocytes recognize foreign antigens

Eosinophil

A white blood cell that can ingest bacteria and other foreign cells, that may help immobilize and kill parasites, that participates in allergic reactions, and that helps destroy cancer cells

Helper T cell

A white blood cell that helps B lymphocytes recognize and produce antibodies against foreign antigens

Histocompatibility

Literally, compatibility of tissue; determined by human leukocyte antigens (the major histocompatibility complex) and used to determine whether a transplanted tissue or organ will be accepted by the recipient

Human leukocyte antigens (HLA)

A group of molecules that are located on the surface of cells and that are unique in each organism, enabling the body to distinguish self from nonself; also called the major histocompatibility complex

Immune response

The reaction of the immune system to an antigen

Immunoglobulin

A synonym for antibody

Interleukin

A type of cytokine secreted by some white blood cells to affect other white blood cells

Killer (cytotoxic) T cell

A lymphocyte that attaches to foreign or abnormal cells and kills them

Leukocyte

A white blood cell, such as a monocyte, a neutrophil, an eosinophil, a basophil, or a lymphocyte

Lymphocyte

The white blood cell responsible for specific immunity, including producing antibodies (by B lymphocytes) ...

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