The Immune System (DP IB Biology)

The Immune System: Innate vs Adaptive

The innate immune system

• The innate immune system is able to recognise and respond to any item that enters the body that is 'non-self'; these items could be:

  • Bacteria

  • Fungi

  • Viruses

  • Protists

  • Pollen grains

  • Dust

• The innate immune system recognises these non-self items because they display, or act as, non-self antigens

  • An antigen is a molecule that can trigger an immune response

  • All cells have antigens on their cell surface membranes

  • An individual's own cells will be recognised due to the presence of self antigens, while a foreign cell will have non-self antigens and so will initiate an immune response

  • Items such as pollen grains, or other allergens, may be recognised by the innate immune system as non-self antigens; this leads to the symptoms of allergy

• Individuals are born with the ability to mount an innate immune response to non-self antigens, and the response does not change during their lifetime

• The action of phagocytes forms part of the innate immune response; phagocytes will engulf and digest any item that displays non-self antigens

• Innate immune responses are sometimes described as non-specific immune responses

  • Innate immune responses are broad in nature; they occur in response to any non-self antigen and are not specific to any one particular type of antigen

The adaptive immune system

• The adaptive immune system responds to the presence of specific non-self antigens, e.g. the antigens of a particular type of pathogen

  • When the adaptive immune system first encounters a new type of non-self antigen, a sequence of events occurs that eventually leads to antibody production and the presence of memory cells in the blood

  • When the adaptive immune system encounters the same type of antigen again, the sequence of events occurs much more quickly and produces many more antibodies, and the pathogen is destroyed before any symptoms occur

• The adaptive immune system changes over the course of an individual's lifetime as they are exposed to different types of antigen

  • A memory of different pathogens is built up as exposure occurs; this is known as immunological memory

  • Young babies have no adaptive immunity, and the adaptive immune system develops with age

• Vaccination makes use of the adaptive immune system by introducing it to new pathogens, therefore speeding up the immune response on the next exposure to the same pathogen

• Adaptive immune responses are sometimes referred to as specific immune responses, as they occur due to the presence of specific antigens