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active immunity — immunity to disease resulting from the production of antibodies.

AIDS (acquired immune deficiency syndrome) — disease resulting from a disorder of the immune system by HIV.

antibody — substance that prevents infection; antibodies are produced by white blood cells in response to an invasion by an organism or substance.

bacteriophage — virus that invades a bacterium.

capsid — outer protein coat of a virus.

DNA (deoxyribonucleic acid) — nucleic acid that carries genetic material and stores the information needed for protein synthesis.

HIV (human immunodeficiency virus) — the virus that causes AIDS.

host — organism in which another organism lives, such as a parasite.

immunity — body?s system of natural resistance to disease.
interferon — substance produced by a cell when it?s invaded by a virus.

lytic cycle — reproductive process in viruses in which the host cell is killed.

lysenogenic cycle — reproductive process in temperate viruses.
microorganism — microscopic organism.

parasite — organism that feeds off other living organisms.

passive immunity — immunity that occurs when a person receives antibodies produced in another person or in an animal that has developed immunity to the disease.

poliomyelitis — viral disease causing stiffness and paralysis that may result in death.

replicate — process in which DNA molecules form exact copies or duplicates.

RNA (ribonucleic acid) — nucleic acid that reads genetic information carried by DNA and guides protein synthesis.

temperate virus — virus that does not immediately cause disease.

tobacco mosaic — virus that infects tobacco and other plants.

vaccination — process in which an antigen is introduced to stimulate the immune system.

virulent — disease-causing agent that is highly infectious.

virus — tiny non-living particle made up of hereditary material and protein.