| Themes > Science > Life Sciences > General Biology > Immunology > Immunity to Infection > Immunity to Infection |
Obviously protecting the host from infection is the raison d'être of the immune system. We have spent the past weeks looking at the molecules and cells of the immune system, in this last lecture I want to try to look at the immune system as an integrated defence mechanism. The first thing to remember is that most microorganisms arriving at the external surfaces of the body fail to establish a colony. Just as in military strategy, the hardest thing for an invader to do is to establish a beachhead. So one cardinal property which distinguishes those species of microorganism which are capable of colonising human hosts from the much larger number which are not is their ability to overcome the physical and physiological barriers which protect the surfaces of the body. Even then the majority of colonising organisms do not penetrate the body's surface and indeed the presence of these harmless commensal bacteria makes a significant contribution to keeping out undesirables. Pathogens, then are that rather select group which can both colonise and invade the body - there are a very small number of exceptions to this (almost all gut bacteria) which can cause disease by secreting toxins which damage the host without the organisms themselves penetrating the body surface. We will consider the problem in two ways. First temporally, looking at the different phases of infection and response. Second we will look at the different classes of pathogen and the importance of different kinds of immunity. |
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