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immune complex

the result of a reaction between an antigen and a specific antibody. This combination of antigen bound by antibody may or may not cause adverse effects in a person.

immune response

the reaction of the immune system to foreign substances.

immune system

the complex system (network of specialized cells and organs) in the body responsible for fighting disease. Its primary function is to identify foreign substances in the body (bacteria, viruses, fungi, or parasites) and develop a defense against them. This defense is known as the immune response. It involves production of protein molecules called antibodies to eliminate foreign organisms that invade the body.


natural or acquired resistance provided by the immune system to a specific disease. Immunity may be partial or complete, specific or nonspecific, long lasting or temporary. Immunity is indicated by the presence of antibodies in the blood and can usually be determined with a laboratory test.


the process by which a person or animal becomes protected against a disease; the process of inducing immunity by administering an antigen (vaccine) to allow the immune system to prevent infection or illness when it subsequently encounters the infectious agent. This term is often used interchangeably with vaccination or inoculation.


a substance capable of provoking an immune response. Also called an antigen.


the ability of an antigen or vaccine to stimulate immune responses.


the rate of occurrence of some event, such as the number of individuals who get a disease divided by a total given population per unit of time.

incubation period

the time from contact with infectious agents (bacteria, viruses, fungi, or parasites) to onset of disease.

IND (investigational new drug)

The pre-approval status of an experimental drug or biologic (e.g., vaccine)after the US Food and Drug Administration (FDA) agrees that it can be tested in people (generally done in order to collect sufficient data for licensure). "IND" often refers to the application to obtain this pre-approval status.


capable of spreading disease. Also known as communicable.

informed consent

an agreement signed by prospective volunteers for a clinical research trial that indicates their understanding of (1) why the research is being done, (2) what researchers want to accomplish, (3) what will be done during the trial and for how long, (4) what risks are involved, (5) what, if any, benefits can be expected from the trial, (6) what other interventions are available, and (7) the participant's right to leave the trial at any time.

IRB (institutional review board)

a committee of physicians, statisticians, community advocates, and others that reviews clinical trial protocols before they can be initiated and is responsible for monitoring the safety of clinical trials at that institution. IRBs ensure that the trial is ethical and that the rights of participants are adequately protected.