/i myooh"ni tee/, n., pl. immunities.1. the state of being immune from or insusceptible to a particular disease or the like.2. the condition that permits either natural or acquired resistance to disease.3. the ability of a cell to react immunologically in the presence of an antigen.4. exemption from any natural or usual liability.5. exemption from obligation, service, duty, or liability to taxation, jurisdiction, etc.: The ambassador claimed diplomatic immunity when they arrested him for reckless driving.6. Law. exemption from criminal prosecution or legal liability or punishment on certain conditions.7. special privilege.8. Eccles.a. the exemption of ecclesiastical persons and things from secular or civil liabilities, duties, and burdens.b. a particular exemption of this kind.[1350-1400; ME immunite < L immunitas. See IMMUNE, -ITY]Ant. 1. susceptibility. 4, 5. liability.
* * *IAbility to resist attack or overcome infection by invading microbes or larger parasites.Immunity is based on the proper functioning of the body's immune system. In natural or innate immunity, immune mechanisms present at birth work against a wide variety of microbes whether or not they have been encountered before. Acquired immune responses, tailored to act against a specific microbe or its products, are stimulated by the prior presence of that microbe. Previous infection with a particular pathogen, as well as vaccines, produce this type of immunity. The mechanisms of innate immunity include physical barriers (including the skin) and chemical barriers (such as bactericidal enzymes present in saliva). Microbes that penetrate the body's natural barriers encounter substances (such as interferon) that inhibit their growth or reproduction. Phagocytes (particle-engulfing cells) surround and destroy invading microbes, and natural killer cells pierce the microbe's outer membrane. Innate immunity does not confer lasting resistance, or immunity, to the body. Acquired immunity is based on the recognition of antigen by B cells and T cells and is activated when innate mechanisms are insufficient to stem further invasion by pathogens. Killer or cytotoxic T cells destroy infected and foreign cells. Helper T cells induce B cells stimulated by the presence of antigen to proliferate into antibody-secreting cells, or plasma cells. Antibodies produced by plasma cells bind to antigen-bearing cells, marking them for destruction. Acquired immunity relies on the long-term survival of sensitized T and B memory cells, which can proliferate quickly upon reinfection by the same pathogen. See also immunodeficiency; immunology; leukocyte; reticuloendothelial system.IIIn law, exemption or freedom from liability.Under international treaty, a diplomatic representative is exempt from local laws, both civil and criminal. In many countries, judges, legislators, and government officials, including the heads of state, enjoy limited or absolute immunity at home to protect them from personal liability for wrongful acts or omissions that arise from the performance of their duties. A public prosecutor may grant immunity from prosecution to a witness who is suspected of criminal activity in return for testimony against other suspected criminals.
* * *▪ lawin law, exemption or freedom from liability. In England and the United States a legislator is immune from civil liability for statements made during legislative debate. He is also immune from criminal arrest, although he is subject to legal action for crime. French law and practice prohibits the arrest of a member of the legislature during a session without authorization by his chamber. This practice prevails in many European and other nations (e.g., Belgium, Switzerland, Italy, Spain, and Japan).Under international treaty, a diplomatic representative is exempt from local jurisdiction, both civil and criminal. This immunity extends to his places of office and residence.A public prosecutor may grant immunity from prosecution to a witness who is suspected of criminal activity in return for his aid in testifying against other suspected criminals. In U.S. law, there are two types of criminal immunity—transactional immunity and use immunity. Transactional immunity, when granted, means that the recipient may not be prosecuted for any aspect of the criminal act in which he was involved. Use immunity means only that the testimony of the immunized person, given in return for immunization, may not be used against that person or coconspirators in a criminal act unknown to the prosecutor prior to the granting of immunity.
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