BIOLOGY Volume 2 - A Guide to General Biology - 2004

14. TRANSPORT IN ANIMALS

14.9. The Immune System

14.9.5. Types of Immunity

Immunity is divided into active and passive. Either of these types can be acquired naturally or artificially. The latter case is referred to as immunization of the Organism.

Natural Active Immunity

This type of immunity is acquired As a result of an infection. The body produces Antibodies itself in response to a foreign agent. Since immunological memory Cells formed During the first encounter with an antigen can rapidly synthesize large amounts of antibodies upon subsequent exposure to the same antigen, this type of immunity is the most effective and usually persists for a long time, sometimes throughout life.

Artificial Active Immunity (Vaccination)

This type of immunity is established by injecting (or less commonly, administering orally) a small (non-harmful) quantity of an antigen into the body as part of a so-called vaccine. This process is called vaccination. If a culture of a pathogenic microorganism is used for vaccination, it is first neutralized by killing or attenuation (see below). The introduced antigen stimulates The formation of corresponding antibodies and memory cells in the body. Repeated vaccination (booster shot) is often required to enhance immunity and prolong its duration. Currently, several types of immunogenic components are used in Vaccines.

1. Toxoids. Toxins (poisons) produced, for example, by tetanus and diphtheria Bacteria, are neutralized (detoxified) with formaldehyde while retaining their antigenic properties. Consequently, the administration of toxoids will stimulate antibody production without causing disease symptoms.

2. Killed Microorganisms (Killed Vaccine). Some killed Viruses and bacteria are capable of eliciting a normal Immune Response and are therefore used for immunization. An example is the Influenza vaccine containing killed Influenza Viruses.

3. Attenuated Microorganisms (Live Attenuated Vaccine). The pathogen is "crippled" in one way or another so that it can no longer cause disease, yet remains capable of reproducing only very slowly. This is referred to as a reduction in its virulence. Attenuation is carried out, for example, by culturing at a higher-than-normal Temperature or by long-term addition of specific chemicals to the culture medium. A pathogen with reduced virulence may also be a mutant strain of the disease-causing agent that is harmless to health yet possesses the same Antigens. Live vaccines are widely used against bacterial infections such as tuberculosis, as well as against measles, mumps, rubella, and poliomyelitis caused by viruses. Smallpox has now been eradicated, but in the past, a live virus was used for protection against it. It was not attenuated, but posed no danger to humans because it was not a "true" pathogen, but a closely related form with low virulence.

4. New Vaccines. For many years, there was no significant progress in vaccine development Methods; however, recent breakthroughs in molecular biology and Introduction/32.html">Genetic Engineering have allowed for new approaches in this field. Antigens are most commonly Proteins, meaning they are encoded by genes. If such a Gene is introduced into a bacterium using the standard method described in Ch. 12, it can be turned into a sort of living factory producing large quantities of the antigen, which will stimulate The production of the required antibodies. Vaccines against cholera, typhoid fever, and hepatitis B are already being prepared in this manner. In some cases, this reduces the risks associated with vaccinations, such as the pertussis vaccine. Another approach is the Chemical synthesis of antigens from Amino Acids, provided their Amino Acid Sequence is known.

Vaccinations are common practice in developed countries and are one of the primary factors that have contributed to such a sharp decline in the incidence of infectious diseases there over the past century. Other reasons for this are linked to improved living standards and environmental sanitation, in particular better Nutrition, advancements in drinking Water purification and sewage Treatment, the control of industrial pollution, and the like.

An example of routine vaccination in the UK is the administration of the combined measles, mumps, and rubella (MMR) vaccine to two-year-old children. It is also recommended to receive three doses of the diphtheria, tetanus, and pertussis (triple) vaccine at various ages. In some countries, vaccination is mandatory. As a result of such prophylaxis, smallpox has been completely eradicated worldwide, and A number of childhood infections such as diphtheria, poliomyelitis, and measles are now extremely rare (Fig. 14.42). It is quite possible that poliomyelitis will be eradicated in the near future. The World Health Organization (WHO), supported by other bodies including UNICEF (United Nations Children's Fund) and the World Bank, has targeted six severe diseases as primary priorities for Prevention in the third world through its Expanded Programme on Immunization: diphtheria, pertussis, tetanus, poliomyelitis, measles, and tuberculosis. Although these infections are no longer considered a serious threat in economically developed societies, they remain deadly and widespread in the rest of the world. Currently, more than 80% of children in developing countries are vaccinated against them. Similar efforts are underway to combat hepatitis B.

Vaccinations against certain infections, particularly influenza, still require substantial improvement, and no vaccine is yet available for a number of diseases, including Cancer, leprosy, malaria, and AIDS, despite intensive research in this direction.

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Fig. 14.42. The Effect of vaccination against diphtheria and measles. A. Mortality of children under 15 years of age from diphtheria and measles in England and Wales from 1885 to 1972 (note that the ordinate scale is logarithmic). Vaccination against diphtheria was introduced in 1940. Within 15 years, this deadly childhood disease was practically eradicated. B. Reported cases of measles in England and Wales from 1950 to 1991. Vaccination began in 1968. The graph shows that small epidemics of measles occur approximately every two years. (A — from Registrar General’s Statistical Review for England and Wales, Part 1, Tables Medical, HMSO (1887-1974) HMSO. B — from The Health of The Nation and You, Dept of Health, HMSO (1992) (source — OPCS).)

Passive Immunity

Passive immunity occurs when antibodies against a specific antigen (pathogen), already produced by one individual, are transferred to another individual. This provides immediate protection, unlike active immunity, which takes days or even weeks to develop. However, such protection is relatively short-lived because antibodies are degraded by normal biochemical processes within the body, causing their levels to gradually decline.

Natural Passive Immunity

Passive immunity can be acquired naturally. For example, maternal antibodies cross the Placenta into the fetal bloodstream, providing protection for the infant while its own immune system is not yet fully functional. Antibodies are also present in colostrum, a mammary secretion received by the infant during the first days of life. Passive immunity is established through the absorption of these protein molecules in the infant's intestine without being broken down.

Artificial Passive Immunity

Antibodies produced in one organism can be extracted and introduced into the Blood of another, even one belonging to a different species. They will protect the recipient against the corresponding pathogen if the disease has already developed or if There is a threat of such an infection. For instance, horses were formerly infected with tetanus and diphtheria, and their blood serum containing antibodies against these disease agents was used for human inoculations. Nowadays, only human serum is administered to humans to induce artificial passive immunity. We now have antibodies available against rabies and certain snake venoms. Such prophylaxis is important not only as a defense against infection. Antibodies against the Rhesus factor (a human erythrocyte antigen in one of the blood group systems) are administered to Rhesus-negative mothers carrying a Rhesus-positive fetus. The rationale behind this Procedure is explained in Section 14.9.8.

Data on the various types of immunity are summarized in Table 14.5.

Table 14.5. Various types of immunity