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## Immunity ### Progress Check 1. Give an example of each of the following: * Germ-killing body secretion: **Lysozyme in tears and saliva** * Germ-trapping body secretion: **Mucus in the respiratory tract** * Mechanical barrier that prevents entry of germs into the body: **Skin**...

## Immunity ### Progress Check 1. Give an example of each of the following: * Germ-killing body secretion: **Lysozyme in tears and saliva** * Germ-trapping body secretion: **Mucus in the respiratory tract** * Mechanical barrier that prevents entry of germs into the body: **Skin** 2. Mention if the following statements are **True** (T) or **False** (F) * Immune system deals with the germs after they have entered the body: **T** * Antibodies eat up the germs: **F** * Human beings can suffer from all those diseases which attack dogs: **F** * Anti-venin injection against snake bite is an example of artificially acquired passive immunity: **T** * Mother's antibodies may reach the foetus through placenta: **T** * A person having once suffered from measles usually gets repeated attacks: **F** ### Vaccination and Immunization Vaccination is the practice of artificially introducing the germs or the germ substance into the body for developing resistance to particular diseases. Scientifically, this practice is called prophylaxis and the material introduced into the body is called the vaccine. The vaccine or germ substance is introduced into the body usually by injection and sometimes orally (e.g. polio drops). Inside the body, the vaccine stimulates the WBCs to produce antibodies against the germs for that particular disease. The terms "vaccine" and "vaccination" were originally used for vaccination against smallpox, but now these are used in a general sense. ### Four Categories of Vaccines 1. Killed germs, e.g. TAB vaccine for typhoid, Salk's vaccine for poliomyelitis, and the vaccine for rabies (dog-bite). 2. Living weakened germs, e.g. the vaccine for measles, and the freeze-dried BCG vaccine for tuberculosis. Full form of BCG is "Bacillus Calmette Guérin" named after two French workers who developed this strain for vaccination. 3. Living fully poisonous germs, e.g. smallpox. In this vaccination, a person is inoculated with cowpox virus which is very similar to smallpox virus. Cowpox virus causes only a single pustule to develop rather than multiple pustules of smallpox all over the body. Vaccination against cowpox protects from smallpox as well. The smallpox vaccinations are no more given, because the disease has been totally eradicated according to present-day records. 4. Toxoids (inactivated toxins secreted by bacteria), e.g. diphtheria and tetanus. These toxins (poisons) are made harmless by the addition of dilute formalin, yet retaining the capacity to produce antibodies (antitoxins). Attempts are being made to develop a vaccine against AIDS also, let us hope we succeed in doing so. ### Vaccination Vaccination is the introduction of any kind of dead or weakened germs into the body of a living being to develop immunity (resistance) against the respective disease or diseases. ### Immunization Developing resistance to disease-producing germs or their toxins by introducing killed germs or germ substances to induce the production of specific antibodies. Immunisation against some common infectious diseases has been done in India on a mass scale with an attempt to cover the entire population. The National Immunisation Schedule is as follows: | Age | Vaccinations | |------|-------------------------------------------------------------------| | 3-12 months | DPT - 3 doses at intervals of 4-6 weeks | | | Polio (oral) - 3 doses at intervals of 4-6 weeks | | | BCG (intradermal) - one dose | | 9-15 months | Measles vaccine - one dose |