Passive and Active Immunity - Essay Example

Immunity Introduction Immunity is the bodys ability to recognize and defend itself against bacteria, viruses, and substances that appear foreignand harmful to the body (Immune response, Medline Plus). The process of strengthening a person’s defence mechanism against infection is known as immunization (Immunization, WebHealthCenter.com). Immunization is a proven tool for controlling infectious diseases (Immunisation, WHO). It is one of the most cost-effective strategies in health care (Nicoll, Elliman & Begg, 1989). Immunity is of 2 types: passive and active. Passive immunity Acquisition of immunity without challenging the immune system with an antigen is known as acquired or passive immunity. This can be done by transfer of serum or gamma globulins from an immune donor. The process of acquisition of passive immunity can be either natural or artificial. Natural immunity occurs when there is transfer of immunity to the fetus from the mother through placental transfer of IgG or colostral transfer of IgA. When immunity is acquired by artificial transfer of immunoglobins, it is known as artificial passive immunity. This occurs when a non-immune person is injected with gamma globulins from other human or animal. Artificial passive immunity is induced as a form of treatment for many conditions like infections and poisoning. Those with hypogammaglobulinemia also are treated similarly. The infections which can be handled with passive immunization are diphtheria, tetanus, measles and rabies (Ghaffar, 2002). Active immunity Immunity produced as result of exposure of the body to antigens is known as active immunity. The active immunity can be natural or acquired. Natural immunity occurs when a person develops immunity following natural exposure to pathogens in the form of clinical or subclinical infection. When the person develops immunity following artificial administration of the antigen in the form of live pahtogen, dead pathogen or a component of pathogen, it is known as artificial active immunization. All vaccines produce artificial active immunization (Ghaffar, 2002). The vaccines used to produce active immunity can be thus classified into live vaccines, killed vaccines and sub-unit vaccines. Live organisms are mainly used for immunization against viral infections. Live vaccines are now available for vaccination against measles, mumps, rubella and chicken pox. Example for live vaccine against bacteria is BCG vaccine (Bacillus Calmet Geurin). Live vaccines act by producing self-limiting non-clinical infections which lead to subsequent immunity, both humoral and cell-mediated. Cell-mediated immunity is essential for intracellular pathogens. Due to this reason, they are contraindicated in immunocompromised persons (Ghaffar, 2002). In killed vaccines, the whole organisms are inactivated by treatment with heat, chemicals or UV irradiation. Examples of killed vaccines are vaccines against yellow fever,influenza, hepatitis-A, cholera, typhoid and pertussis. Sub-unit vaccines are those which consist of subcomponents of the pathogenic organisms. These are usually either proteins or polysaccharides and they induce immunity to the whole organism. The polysaccharides are relatively weak T-independent antigens. They produce only IgM responses. Hence there will be no immunologic memory when immunity is induced with them. To make them more immunogenic, they are often combined with proteins. This is known as conjugation. Examples of such vaccines are vaccines against haemophilus, pertussis, meningococcus and pneumococcus. Vaccines against hepatitis-B and rabies are proteins parts of the organisms cloned into a suitable vector. This is done to reduce risk of infection. Vaccines against diphtheria, tetanus and cholera used modified version of their toxins, known as toxoids to induce immunity. The toxoid is nothing but the toxin, but without toxic properties (Ghaffar, 2002). Eradication of diseases using vaccines Currently, smallpox is the only disease that has been eradicated throughout the world. The success of its eradication can be attributed to small pox vaccine and the mass immunization programme. The vaccine helps the body develop immunity to smallpox. It consists of a live virus called vaccinia which resembles the pox virus. It induces active immunity against small pox but cannot cause the disease. It has many beneficial features contributing to the success of eradication. The most important feature is that the vaccine induces a high level immunity for 3 to 5 years. Thereafter, the immunity decreases, but revaccination leads to longer immunity. The vaccine has been effective in preventing smallpox infection in 95% of those vaccinated. Another feature is that the vaccine prevents or lessens the severity of infection when given within a few days of exposure. In the sense, it is useful for post-exposure prophylaxis also. Mass immunization was useful in eradicating small pox because, small pox cannot propagate in any other animal other than humans. Hence, once the human cases were completely suppressed, the disease was eradicated. Also, no mutations occurred in the small pox virus. Similar is the case with polio virus which is on its way to get eradicated by mass immunization. Mass immunization protects a population in excess of the immunity acquired to each individual (Sargent, 2005). Despite many trials and research, no successful vaccine has been developed against malaria. There are many reasons for this: 1. Parasites are more complex organisms than bacteria and viruses. They have more complicated structures and life-cycles. Thus, an ideal vaccine dealing with parasites like malaria would need to be effective against multiple targets which is not practical. 2. Plasmodium falciparum keeps evolving continuously. So it is difficult to produce a vaccine that is update with the evolution. 3. There are two main types of immune response than could be elicited by the parasite. These are Anti-parasitic Immunity and Anti-toxic Immunity. The anti-Parasitic Immunity consists of an antibody response (humoral immunity) and a cell-mediated immune response. Hence, the kind of vaccine that needs to be developed should be able to produce more of cell-mediated immunity which is difficult. 4. Since the vaccine needs to be targeting several antigens, it may require delivery to different areas and by different means in order to elicit an effective response. 5. The life cycle of malarial parasite is complex. 6. Lack of full understanding of mechanisms of malaria infection 7. Inadequate resources and limited private-sector involvement 8. Uncertain mechanisms for procuring and distributing a successful vaccine (Media Centre, WHO 2006) Currently DNA vaccines are developed against malaria. These vaccines are developed by removing sections of DNA from the parasitic genome and inserting the sequences into a vector. The vectors used for this purpose are plasmid genomes, attenuated DNA viral genomes, liposomes, proteoliposes, and some complex molecules. When the subunit vaccine thus produced is endocytosed into a host cell, the DNA sequence is then incorporated into the host DNA and replicated by protein synthesis. In many countries, child health and immunization has low priority. The economic conditions of underdeveloped countries force them to concentrate on other aspects of living. Also, in some parts of the world, unnecessary advertisement about the harmful effects of vaccination prevents parents from vaccinating their children. Poor literacy and education levels also contribute to failure of vaccination. Inappropriate information imparted by health service personnel to the parents prevents them from giving their children vaccination (Nicoll, Elliman & Begg, 1989). Gene technology is now employed to produce newer vaccines. This technology is now being used to make vaccines against HIV and malaria. It is has been proposed that DNA containing one or more genes of the organism to which immunity is sought is injected into the body of the human and the DNA thus introduced is anticipated to enter the cell nuclei and program synthesis of immune response to the particular organism (Sargent 2005). Conclusion Immunity is the body’s ability to keep away from infections. This can be either artificial or naturally developed, or active or passive. Vaccination is provides active artificial immunity against the disease sought for immunity. Live, dead or a part of pathogens can be used for vaccination. The success of vaccination depends on the country’s strategy towards immunization, acceptance rates in the society, the efficacy of vaccine and the lifecycle of the organism against which vaccine is sought. The latest technology in vaccination is gene technology. References Ghaffar, A (2002). Immunisation. Retrieved May 1, 2008 http://pathmicro.med.sc.edu/pdfimm2002/02Immunization.pdf Immune response. Medline Plus. Retrieved May 1, 2008 http://www.nlm.nih.gov/medlineplus/ency/article/000821.htm Immunization. WebHealthCenter.com. Retrieved May 1, 2008 http://www.webhealthcentre.com/general/immunisation_index.asp Immunisation. World Health Organisation. Retrieved May 1, 2008 http://www.who.int/topics/immunization/en/ Media Centre. (2006). Global strategy aims for effective malaria vaccine by 2025. World health organisation. Retrieved May 1, 2008 http://www.who.int/mediacentre/news/notes/2006/np35/en/index.html Nicoll, A., Elliman, D., & Begg, N.T. (1989). Immunization: causes of failure and strategies and tactics for success. BMJ, 299(6703), 808–812. Sargent, M.G. (2005). Biomedicine and the Human Condition: Challenges, Risks, and Rewards. Cambridge: Cambridge University Press, p.185-189 Read More