WJEC Biology for A2: Student Bk

Going further The word vaccination is derived from vacca, Latin for a cow, recalling the work of Edward Jenner, who vaccinated against smallpox using cowpox, a related but less dangerous pathogen. St u dy point In active immunity the body makes its own antibodies. In passive immunity, the body receives antibodies made elsewhere. St u dy point The most successful vaccines, e.g. the smallpox vaccine, are for pathogens with only one antigenic type, and are highly immunogenic. Knowledge check Match the terms 1–4 with their meanings, A–D. 1. Antibody. 2. Plasma cell. 3. Vaccine. 4. Passive immunity. A. A differentiated B lymphocyte that secretes antibodies. B. Short-term immunity due to the introduction of antibodies made by another person. C. A Y-shaped protein produced in response to a specific antigen. D. An inactive or weakened pathogen, or one of its proteins, used to produce active immunity against a disease. 46 Passive immunity The body receives antibodies produced by another individual in passive immunity. This happens naturally when they are transferred: ▪ From mother to foetus across the placenta. ▪ To the baby in breast milk. Antibody injections, sometimes called Ig (immunoglobulin) replacement therapy, are given in various situations, including: ▪ When rapid resistance is needed, and there is no time for the active immune response to develop, e.g. when someone is bitten by an animal infected with rabies; a wound in which the risk of tetanus is very high; for an urgent visit to a part of the world where an infection is endemic, e.g. armed forces personnel who have to travel without warning. ▪ Cases of PIDD (primary immune deficiency disease) and cases of acquired immunity conditions, e.g. HIV-AIDS, in which patients do not make enough antibodies and so cannot provide enough protection for themselves against pathogens. The protection given by injected antibodies is short lived because the body mounts an immune response against them, as they are recognised as foreign. In addition, the individual receiving the antibodies does not have any relevant memory cells. Effectiveness of vaccination Some vaccines are more effective than others. So to provide long-lasting immunity, vaccines against different diseases have different schedules. Some formulations of the HPV vaccine, for example, need only one dose; the vaccine against meningitis B is given in three doses; influenza vaccinations are given annually to older people. For a vaccination to protect successfully against disease: ▪ The antigen should be highly immunogenic. This means that a single dose of the vaccine would cause a strong response from the immune system. It would rapidly make a large number of antibody molecules, specific for a particular antigen, e.g. Vaccinia virus, a close relative of Variola major , the smallpox virus, used to make smallpox vaccine. ▪ There should be only one antigenic type (serotype) of the pathogen, e.g. Rubella , the virus that causes one type of German measles. All Rubella viruses have the same surface antigens so only one vaccine is needed and the antibodies formed are able to attack all of them. The ‘flu A virus has many serotypes because it undergoes genetic recombination and frequent mutation. The memory cells produced in the first exposure may not be stimulated in a subsequent exposure if the virus has mutated. A different vaccine may, therefore, be needed for each antigenic type and the small changes in the antigens generated by mutation mean that a vaccine may not be totally effective. WORKING SCIENTIFICALLY With the understanding that antibodies bind selectively to specific molecules, uses have been devised which do not relate to their ability to attack pathogens, including: • An advance in cancer treatment, which uses antibodies attached to chemotherapy drugs to deliver the drugs directly to tumour cells. • A potential treatment for some types of migraine involves injecting antibodies against a characteristic protein. Option A: Immunology and disease 275