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Immunity (medical)

From Wikipedia, the free encyclopedia

In biology, immunity is the state of having sufficient biological defences to avoid infection, disease, or other unwanted biological invasion. It is the capability of the body to resist harmful microbes from entering it. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide range of pathogens irrespective of antigenic specificity. Other components of the immune system adapt themselves to each new disease encountered and are able to generate pathogen-specific immunity.

The concept of immunity has intrigued mankind for thousands of years. The prehistoric view of disease was that it was caused by supernatural forces, and that illness was a form of theurgic punishment for “bad deeds” or “evil thoughts” visited upon the soul by the gods or by one’s enemies.^[1] Between the time of Hippocratesand the 19th century, when the foundations of the scientific methods were laid, diseases were attributed to an alteration or imbalance in one of the four humors (blood, phlegm, yellow bile or black bile).^[2] Also popular during this time was the miasma theory, which held that diseases such as cholera or the Black Plague were caused by a miasma, a noxious form of "bad air".^[1] If someone were exposed to the miasma, they could get the disease.

The modern word “immunity” derives from the Latin immunis, meaning exemption from military service, tax payments or other public services.^[3] The first written descriptions of the concept of immunity may have been made by the Athenian Thucydides who, in 430 BC, described that when the plague hit Athens “the sick and the dying were tended by the pitying care of those who had recovered, because they knew the course of the disease and were themselves free from apprehensions. For no one was ever attacked a second time, or not with a fatal result”.^[3] The term “immunes”, is also found in the epic poem “Pharsalia” written around 60 B.C. by the poet Marcus Annaeus Lucanus to describe a North African tribe’s resistance to snake venom.^[2]