Pathogens produce the symptons of an infectious disease by damaging the body's cells or producing poisonous waste products called toxins.
The body protects itself by producing antibodies, which lock onto antigens on the surface of pathogens such as bacterium. This kills the pathogen.
Human white blood cells produce antibodies, resulting in active immunity. This can be a slow process but has a long-lasting effect. Vaccinations using antibodies from other human or animal result in passive immunity, which has a quick but short-term effect.
Each pathogen has its own antigens, so a specific antibody is needed for each pathogen.
The process of immunisation is also called vaccination - It starts with injecting a harmless pathogen carrying antigens. The antigens trigger a response by white blood cells producing the correct antibodies. Memory cells (a type of T-lymphocyte cell) remain in the body, providing long lasting immunity to that disease.
Immunisation carries a small risk to the individual, but it avoids the potentially lethal effect of the pathogen, as well as decreasing the risk of spreading the disease.
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