In this article we will discuss about the historical perspectives and types of immunity.
Historical Perspectives of Immunity:
The phenomenon of immunity (Latin immunis means ‘exempt’) can be traced back to Thucydides, the great historian of Peloponnesian War. In 430 BC he wrote that a plague spread in Athens, only those could nurse the sick who recovered from the plague and could not contract the disease second time.
In the 15th century the first recorded attempts were made by Chinese and Turks to induce immunity deliberately through a technique called variolation. In this method dried crusts from smallpox pustules were either inhaled or inserted into small cuts in the skin.
In 1718, Lady Mary Wortley Montague (wife of a British Ambassador) performed variolation on her own children and observed its positive effect. In 1798, Edward Jenner, an English physician significantly improved the method.
He introduced the fluid from a cowpox pustule into the milk maids and others having smallpox and protected them. He intentionally infected a 8-year old child with fluid from a cowpox pustule and then smallpox. The child did not develop smallpox.
A major advancement was made in the area of immunology by Louis Pasteur. He cultured pathogenic bacteria causing cholera and demonstrated that chickens injected with cultured bacteria developed cholera. Surprisingly, when he injected the chickens with old culture of cholera, the chickens became ill; thereafter they got recovered.
When such chickens were injected with fresh culture of cholera, the chickens were completely protected from the disease. Pasteur put forth a hypothesis that the ageing has weakened the virulence of the pathogen.
Hence such attenuated or weakened strain might be administered to protect the disease. He called such attenuated strain of pathogens as vaccine (Latin vacca means cow) in the honour of Jenner’s work with cowpox inoculation.
Pasteur extended his findings to other diseases by attenuating the pathogenic strains. In 1881, Pasteur vaccinated one group of sheep with heat-attenuated anthrax bacillus (Bacillus anthracis). Then he challenged the vaccinated sheep and some unvaccinated sheep with a virulent culture of the Bacillus.
He noted that all the vaccinated sheep survived. This experiment became a milestone in the area of immunology. In 1885, Pasteur administered his first vaccine to a young boy bitten by a rabid dog who survived and later became the custodian at the Pasteur Institute.
In 1890, Emil von Behring and S. Kitasato first gave the mechanism of immunity. In 1901, von Behring was awarded with Nobel Prize in medicine. He demonstrated that the serum (non- cellular component of coagulated blood) from animals, previously, immunized to diphtheria, transferred the immune state to un-immunized animals.
The active state of immune serum could neutralize the toxin of bacteria, hence it was also named as antitoxin. Developments made during 20th century are most significant. The names of Nobel Prize winners in the area of immunology are listed in Table 22.1
Types of Immunity:
Immunity is of two types, naturally acquired immunity and artificially acquired immunity.
1. Naturally Acquired Immunity:
Naturally acquired immunity (NAI) is of two types, naturally acquired active immunity and naturally acquired passive immunity.
(i) Naturally Acquired Active Immunity:
Naturally acquired active immunity is obtained when a person is exposed to antigens in the course of daily life and the immune system responds by producing antibodies and specialized lymphocytes. For some diseases immunity is life long for example, measles, chicken pox and yellow fever.
(ii) Naturally Acquired Passive Immunity:
Naturally acquired passive immunity involves the normal transfer of antibodies from a mother to her infants. An expectant mother is able to pass some of her antibodies to her foetus across the placenta. This mechanism is called placental transfer.
If the mother is immune to such diseases as diphtheria, rubella or polio, the newly borne infant will be immune to these disease. Certain antibodies also pass to her nursing infant to breast milk, especially in first secretion called colostrum. In the infant, generally the immunity costs only as long as the transmitted antibodies are active usually a few weeks or months.
2. Artificially Acquired Immunity:
Artificially acquired immunity is of two types, artificially acquired active immunity and artificially acquired passive immunity.
(i) Artificially Acquired Active Immunity:
Previously prepared antigens are injected into the susceptible individual who produces antibodies and specialized lymphocytes. This process is known as vaccination or immunization.
(ii) Artificially Acquired Passive Immunity:
It involves injection of immune serum in the susceptible individuals. A person bitten by snake might be injected with antibodies from a horse that is immune to snake venom.