The immunity of the human body is based on ‘memory’. When the body encounters a pathogen for the first time, it reacts with a primary immune response and produces memory cells. When the body is attacked by the same pathogen twice, these memory cells offer an intensified secondary immune response. This memory of the immune system is also used as a principle in the immunisation programme.
A preparation of antigenic proteins of pathogens or an inactive is introduced into the body as a vaccine.The antibodies produced in the body against these pathogens are then able to neutralise the pathogens during an actual infection. Vaccines generate memory, which enables B and T cells to recognise the pathogen quickly and produce an army of antibodies in response. Sometimes, when a quick immune response is required, for instance tetanus, snakebites, preformed antibodies are injected into the body. This type of immunisation, involving preformed antibodies, is called passive immunisation. New technologies like recombinant DNA technology have made the large-scale production of antigenic polypeptides of pathogens from yeast or bacteria possible. The Hepatitis B vaccine is produced in a similar manner from yeast. In higher vertebrates like human beings, memory-based acquired immunity is so evolved that that they can differentiate foreign organisms such as pathogens from self-cells. Sometimes, due to genetic or other unknown reasons, the body attacks itself. This attack damages the body and is called an auto-immune response.For example, rheumatoid arthritis, allergy. An allergic reaction is caused by the release of chemicals like histamine and serotonin from mast cells. Therefore, the use of drugs like anti-histamine, adrenalin and steroids quickly reduces the symptoms of an allergy. To determine the exact cause of an allergy, the patient has to either be exposed to or injected with small doses of different allergens.
Somehow, modern-day lifestyles that border on unhealthy have lowered natural immunity and heightened our sensitivity to various allergens. Moreover, a protected early childhood doesn’t prepare the human body for the vagaries of the environment in a metro city. Therefore, even though our environment is continually getting polluted and we are exposed to thousands of antigens every day, it is a combination of the body’s immunity and a vaccination programme based on immunisation principles that help us combat infections and diseases.