ETYM Latin immunitas, from immunis free from a public service; pref. im- not + munis complaisant, obliging, cf. munus service, duty: cf. French immunité. Related to Common, Mean.
The protection that organisms have against foreign microorganisms, such as bacteria and viruses, and against cancerous cells (see cancer). The cells that provide this protection are called white blood cells, or leukocytes, and make up the immune system. They include neutrophils and macrophages, which can engulf invading organisms and other unwanted material, and natural killer cells that destroy cells infected by viruses and cancerous cells. Some of the most important immune cells are the B cells and T cells. Immune cells coordinate their activities by means of chemical messengers or lymphokines, including the antiviral messenger interferon. The lymph nodes play a major role in organizing the immune response.
Immunity is also provided by a range of physical barriers such as the skin, tear fluid, acid in the stomach, and mucus in the airways. AIDS is one of many viral diseases in which the immune system is affected.
Immunity has been studied mostly in higher vertebrates, especially rodents, domestic animals, and primates.
The quality of being unaffected by something.