A particle composed of a piece of genetic material—RNA or DNA—surrounded by a protein coat. Viruses can reproduce only in living cells.
A blood vessel that carries blood to the heart from the body tissues.
A preparation that stimulates an immune response that can prevent an infection or create resistance to an infection. Vaccines do not cause disease.
A microscopic living organism. Examples include bacteria, protozoa, and some fungi and parasites. Viruses are also called microbes.
Disease that results when the immune system mistakenly attacks the body’s own tissues. Examples include multiple sclerosis, type 1 diabetes, rheumatoid arthritis, and systemic lupus erythematosus.
An agent produced in plants and bacteria, normally very damaging to cells.
Prominent oval masses of lymphoid tissues on either side of the throat.
A family of proteins important for first-line immune defenses against microbes.
A state of immune nonresponsiveness to a particular antigen or group of antigens.
A group of similar cells joined to perform the same function.