MadSci Network: Immunology |
There is a nice article about vaccination at Wikipedia (http://en.wikipedia.org/wiki/Vaccine). There you can find that: "A vaccine is a biological preparation that establishes or improves immunity to a particular disease. A vaccine typically contains a small amount of an agent that resembles a virus or other microorganism. The agent stimulates the body's immune system to recognize the agent as foreign, destroy it, and "remember" it, so that the immune system can more easily recognize and destroy any of these microorganisms that it later encounters." Also, there is written that: "Vaccines are dead or inactivated organisms or purified products derived from them. There are several types of vaccines currently in use. These represent different strategies used to try to reduce risk of illness, while retaining the ability to induce a beneficial immune response." Thus if you think about making vaccine against some virus you are supposed to preserve its antigenic properties and to avoid its virulent (disease-provoking, killer, destructive) properties. To this end, you can kill the virus, or genetically modify it so that it is not virulent any more, or make recombinant antigens of the virus, or perform some other manipulation. Regarding immune system, successful vaccination procedure means that the elements of the immune system recognize the virus, react to it by means of adaptive immune response and produce a long-term memory that protects against real infection by the same virus. For this it is not important to have intact virus or all the components of the virus. This fact is used to make vaccines that contain the parts of the virus that are to be recognized by immune system, and that do not contain the dangerous disease-provoking parts of the same virus. Efficiency of the protection is mostly about immunological memory. If you understand how the immunological memory works, you will understand how vaccination works. Now, our comprehension of immunological memory is far from complete, and there are still things to be resolved. However, in many textbooks of immunology you can find current opinion about immunological memory and vaccination. For the beginning, Wikipedia can help you as well (http://en.wikipedia.org/wiki/Immunological_memory). And for the direct answer to your question. Antigen presenting cell will have to eat virus or its parts present in vaccine, they will have to process it and to present virus-specific antigens to T helper (Th) cells which will then help antigen-specific B cells that have already recognized virus-specific antigens to produce antibodies and to differentiate into memory B cells. Viral particles or parts that were present in the vaccine will be eliminated from the body and memory Th and B cells will stay for a long period, ready to react fast and strongly against possible infection by the same virus. A small problem is that a virus is intracellular pathogen and it would be very nice if vaccination would also provoke cytotoxic T cell (Tc) response, as this would make also Tc memory cells ready to respond to the intracellular infection. However, this is not so easy to achieve, as modification of virus in order to make it non-virulent usually interferes with its capability to infect cells. Some vaccines containing attenuated virus particles accomplish both B and Tc response. Whatsoever, if vaccine is provoking just the B cell memory, it is still protective, as antibodies produced by B cells prevent infection of cells by the virus. You can find additional data about the topic in regular textbook of Immunology (Cellular and Molecular Immunology, by Abul K. Abbas, MBBS, Andrew H. Lichtman, MD, PhD and Shiv Pillai, MD)
Try the links in the MadSci Library for more information on Immunology.