Glossary of Terms
antibiotics—medicines that damage or kill bacteria and are used to treat some bacterial diseases.
antibodies—molecules (also called immunoglobulins) produced by a B cell in response to an antigen. When an antibody attaches to an antigen, it destroys the antigen.
antigen—a substance or molecule that is recognized by the immune system. The molecule can come from foreign materials such as bacteria or viruses.
B cells—small white blood cells crucial to the immune defenses. Also known as B lymphocytes, they come from bone marrow and develop into blood cells called plasma cells, which are the source of antibodies.
cell—the smallest unit of life; the basic living unit that makes up tissues.
disease—a state in which a function or part of the body is no longer in a healthy condition.
DNA (deoxyribonucleic acid)—a complex molecule found in the cell nucleus that contains an organism’s genetic information.
epidemic—a disease outbreak that affects many people in a region at the same time.
genes—units of genetic material (DNA) that carry the directions a cell uses to perform a specific function.
genomes—all of an organism’s genetic material. A genome is organized into specific functional units called genes.
HIV (human immunodeficiency virus)—the virus that causes AIDS.
immune response—reaction of the immune system to foreign invaders such as microbes.
immune system—a complex network of specialized cells, tissues, and organs that defends the body against attacks by disease-causing microbes.
immunity—protection from germs.
immunization—vaccination or other process that induces protection (immunity) against infection or disease caused by a microbe.
infection—a state in which disease-causing microbes have invaded or multiplied in body tissues.
infectious diseases—diseases caused by microbes that can be passed to or among humans by several methods.
inflammation—an immune system process that stops the progression of disease-causing microbes, often seen at the site of an injury like a cut. Signs include redness, swelling, pain, and heat.
microorganisms—microscopic organisms, including bacteria, viruses, fungi, plants, and animals.
microscopic—too small to be seen with the naked eye.
molecules—the smallest physical units of a chemical substance that still keep the chemical properties of that substance; molecules are the building blocks of a cell. Some examples are proteins, fats, carbohydrates, and nucleic acids.
organisms—individual living things.
pandemics—diseases that affect many people in different regions around the world.
parasites—plants or animals that live, grow, and feed on or within another living organism.
pathogens—disease-causing organisms.
protein—a chain of small chemical compounds called amino acids.
RNA (ribonucleic acid)—a complex molecule found in the cell cytoplasm and nucleus. One function of RNA is to direct the building of proteins.
rotavirus—a group of viruses that can cause digestive problems and diarrhea in young children.
T cells—small white blood cells (also known as T lymphocytes) that direct or directly participate in immune defenses.
tissues—groups of similar cells joined to perform the same function.
toxins—agents produced by plants and bacteria, normally very damaging to human cells.
vaccines—substances that contain parts of antigens from an infectious organism. By stimulating an immune response (but not disease), they protect the body against subsequent infection by that organism.
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