Write short note on the following-
Vaccine.

Explanation

Vaccine means prepration of antigenic proteins of pathogens ie.. inactivated or weakened pathogens which are injected into body.
Antigens of vaccine generate primary immune response and the memory B and T cells. When vaccinated person is attacked by same pathogen the existing memory T or B tells recognise the antigen quickly and massive production of lymphocytes and antibodies is done.
Vaccination is based on property of memory of the immune system. Antigenic proteins of pathogen or weakened pathogens are introduced in the body. Body produces antibodies which would neutralise the pathogenic agents when actual infection will be there. Also vaccines generate B and T cells that recognise the pathogen quickly on subsequent exposure.
Passive immunisation.
When quick immune response is required then pre-formed antibodies are directly given to the patients. This is called passive immunisation e.g.. For tetanus and snake bite.
Vaccines are also classified as follow :-
First generation vaccines. These vaccines are produced by conventional technique using vshole microorganisms. These are never of uniform quality and produce side effects.
Second generation vaccines. These vaccines are prepared by recombinant DNA `"technique"//"Genetic"` Engineering. Examples : Hepatitis B virus vaccine. Herpes virus vaccine. Pneumonia vaccine. The yeast-derived recombinant hepatitis B virus vaccine is the first commercially available human vaccine produced by the genetic engineering technology.
Third generation vaccines (= Synthetic Vaccines). These are chemically synthesized multivalent vaccine. These vaccines have high purity. Examples : Vaccine against diphtheria toxin developed by Audibert et al. 1981. Leukaemia Virus Vaccine etc.