[priyasaravanan_1406]

The unique environment of the human and animal body like presence of warmth, moisture and nutrients makes them a perfect habitat for various bacteria and viruses. In order to compete all the pathogens and survive and execute its function properly body has to protect itself by developing a defensive mechanism against all the invading pathogens. So developed defensive system of the body is called as Immune System and the collective study of immune system – its components, functions, response developed against an infection, protection from a disease all falls under one roof called as ‘Immunology’.

The two factors governing the immune system are detection and reaction. Detection is the recognition and identification of the molecule foreign to the body and once detected, a reaction is developed (Immune response) to eliminate the foreign substance. The immune response otherwise known as effector response is the reaction developed by the immune system towards a pathogen entering the system for the first time. The pathogen is either destroyed or neutralized by the effector response of the immune system and the response is stored in the intelligence of the immune system. Recurrence of the exposure of the body to the same pathogen initiates the memory response of the immune system which enhances the immune response.

The article by Thucydides on Plague in Athens around 430 B C could be the first citation on immunology. During that time, the practice of people recovered from the plague infection serving the affected people was observed. But it was correlated to the phenomenon of immunity in later years. It took 2000 years from then to apply this phenomenon in medical field. In China around 15th century in an attempt to develop immunity against the deadly disease small pox, people were either made to inhale the dried crust of the pustules from small pox affected people or it was injected into the body through wounds and this method was coined as Variolation. The beneficial effect of variolation was addressed by Lady Mary Wortley Montagu in 1718. The fame goes to the English physician Edward Jenner for his establishment of the Variolation technique in 1798. He observed milkmaids acquired cow pox disease showing resistance to small pox and validated his observation by experimenting on an eight year old boy by injecting him with cowpox causative and tested for his defense against smallpox.

The further development of immunology has a foot step of the scientist Louis Pasteur whose discovery of immunity to cholera is an interesting story. He cultured the organism potential to cause fowl cholera in his laboratory and introduced this organism deliberately into healthy chicks and observed infection in the birds. After a while return to his laboratory from a short vacation, he used the old culture to infect the chicks and to his wonder the chicks did not develop any signs of infection. He again allowed the growth of the old culture under laboratory condition and injected them into previously infected chickens and found the chickens ability of protection from the disease. This act of Pasteur made him understand that aging of the culture has reduced the virulence of the pathogen and hence it can be used as a protective agent against disease. Pasteur conducted his first vaccination programme in 1881 using Bacillus anthracis a causative agent of anthrax, on sheeps which initiated the further development of immunology. Also in the year 1885, Pasteur’s attempt to vaccinate a boy against Rabies was successful. Inspite of the discovery of vaccination by Louis Pasteur, the insight into the phenomenon behind immunity was well established by a scientist named Emil ven in 1890.

The discovery of immune cells the WBC and Serum component antibody lead to the debate by researchers on cell mediated immunity and immunity produced by antibody (Humoral immunity) until the inter related roles of the immune cells and the antibody in developing immunity were understood. The various researches and discoveries like, the discovery of serum antitoxin, understanding the cellular immunity in Tuberclosis, role of phagocytosis, Type I anaphelaxis hypersensitivity reaction, complement mediated bacteriolysis, discovery of human blood groups, vaccine for yellow fever, antihistamines, research on acquired immunological tolerance, study on the chemical nature of antibodies, immunological techniques like radio immuno assay, immunogenetics (histocompatibility antigens), production of monoclonal antibodies and study on gene rearrangement in antibody production, immune response in transplantation, specific cell mediated immunity and vaccine for human Papilloma virus cites the drastic progress of immunology in the 20th century and its applications.