When we say immune system, white blood cells (WBCs) immediately come to our minds. However, they are just one of the many characters involved in conferring immunity. What is immunity then?
We are protected or equipped to ward off or fight foreign and harmful entities entering our body as a result of our very elaborate immune system. This protection bestowed upon us by our immune system is ‘immunity’.
Immunity can be actively or passively developed within us. Active immunisation occurs due to natural circumstances, in which immunity is transferred from mother to child or when we encounter an infection for the second time by the same pathogen (first encounter confers memory-based immunity). As the name suggests, the immune system of the body plays an active role in developing immunity. Passive immunity is acquired by injecting preformed antibodies against the foreign entity as a preventive measure.
Active immunisation is more beneficial than passive immunisation as it displays memory response in the case of future encounters with pathogens whereas the latter is more of a transient protective measure with no case of memory response in the future.
What are vaccines? Vaccines can comprise inactivated or killed micro organisms, purified toxic products derived from pathogenic organisms which are capable of eliciting an immune response in the body similar to one caused by the live organism without pathogenesis, i. e. without resulting in the diseased condition. Vaccines help induce active immune response in the body against the desired pathogen, thus helping in prevention of pathogenesis and are prophylactic in nature. Edward Jenner administered the first vaccine in 1796, by using cowpox to confer immunity against smallpox in humans. Vaccines can be produced or designed by several methods, some of the types are
1) Attenuated vaccines — These are constituted of microorganisms that have lost the capacity to cause disease but retain their ability to grow within the host. Microorganisms are grown under abnormal conditions for prolonged periods, which often results in the loss of pathogenecity. Recently, genetic engineering techniques are being used to selectively remove genes responsible for pathogenecity. An example for this is the BCG (Bacillus Calmette-Guerin) vaccine against tuberculosis which is an attenuated strain of the Mycobacterium bovis.
2) Inactivated or Killed vaccines — These include microorganisms or pathogens inactivated by heat or chemical treatment. These are comparatively less effective compared to attenuated vaccines and hence require multiple booster doses, for instance, the Salk Polio vaccine.
3) Purified molecules as vaccines — These consist of inactivated toxins, polysaccharides or recombinant or modified microbial antigens or proteins. Certain peptides which bring about an immune reaction in the body are synthesised or incorporated in non pathogenic or attenuated organisms (vectors) and used as subunit vaccines.
4) DNA vaccines — These are genes or DNA segments encoded for antigenic proteins, which on incorporation into the host cells express the coded proteins and confer immunity.
Vaccines may be monovalent — designed to immunise against a single microorganism — or multivalent — providing immunity against more than one strain or microorganisms or two different pathogens.
In recent times, a novel category of vaccines has surfaced which is therapeutic in nature. Cancer is caused when the immune system is not able to control and neutralise abnormally proliferating cells in the body. Cancer vaccines are those which either prevent the development of cancer in high risk individuals or act on existing cancer. Currently, only vaccines against cervical cancer i. e., HPV (human papilloma virus) vaccine exist.
Vaccines are generated by long and tedious procedures involving several stages. Despite the development of innumerable vaccines against different microorganisms, there are many diseases against which vaccines need to be produced such as HIV and malaria.
There is a need for the development of more and more vaccines to boost our immunity against the countless pathogenic threats.
As you can see, prevention is always better than cure!