WJEC Biology for A2: Student Bk

YOU SHOULD KNOW › › › ››› The differences between active and passive immunity ››› That vaccines have different degrees of efficacy ››› The ethical considerations associated with vaccination programmes Key Term Vaccine : A weakened or killed pathogen, or a toxin or antigen derived from it, which stimulates the immune system to produce an immune response against it without causing infection. The secondary immune response The secondary response relies on memory cells and may protect against an identical antigen, even many decades after the first exposure. ▪ On re-exposure to even a small amount of an antigen, after a short latent period, memory cells undergo clonal expansion, but faster than in the primary response. ▪ Antibodies are made more quickly, and are up to 100 times more concentrated than in the primary response. ▪ They remain at high concentration in the circulation for longer and no symptoms develop. Graph showing immune response Active and passive immunity Active immunity The body makes its own antibodies in active immunity, stimulated by either infection or vaccination. It is long lasting because the response produces memory cells. Vaccination When you are vaccinated, the cell-mediated and humoral responses are initiated, even though there is no harmful pathogen present. Vaccines can be: ▪ Antigens isolated from the pathogen, e.g. human papilloma virus (HPV) vaccine. ▪ Weakened or ‘attenuated’ strains of the pathogen, e.g. measles, mumps, rubella (MMR) combined vaccine. ▪ Inactive or killed pathogen, e.g. whooping cough vaccine. ▪ Inactivated toxin, e.g. tetanus vaccine. The vaccine is recognised by the body as being non-self and the immune system behaves as it would if a pathogen were present. This is ‘active’ immunity as the body is making its own antibodies. Over time, the number of memory cells decreases if the body is not exposed to the antigen again. So in some cases, one or more boosters are given, e.g. a tetanus booster every 10 years is recommended. A booster is a further exposure to the vaccine and the response is faster, bigger and longer lasting than the first. More memory cells are made and so the body is protected for longer. time antibody concentration in blood SECONDARY RESPONSE PRIMARY RESPONSE second exposure rst exposure latent period short latent period WJEC A2 Biology: Chapter 14 274