Other innate immune system actions

Alongside the innate system response of inflammation, there are two other key responses that help the innate system respond more effectively to pathogens.

  • Interferons are released during viral infections and act as chemical signals to both warn other nearby cells and enhance the actions of cells fighting the virus from within. Interferons also recruit phagocytes and natural killer cells.
  • Complement proteins help with opsonisation for more effective phagocytosis by phagocytes as well as directly attacking some types of pathogens.

Both interferons and complement proteins trigger inflammation in order to recruit more innate immune system cells and proteins to the area of infection.

Use this page to revise the following concepts within other innate immune system actions:

Interferons

Interferons are a type of signalling cytokine and antiviral protein. They are a key part of our immune system’s defense against viruses. They are commonly released by any cells infected by a virus and can also be released by uninfected leukocytes when a virus is detected. They act as chemical signals to enhance antiviral actions of cells and directly as antiviral proteins that interfere with viral entry to and replication inside an infected cell.

Depending on the type of virus, interferons can inhibit:

  • transcription of viral DNA
  • translation of viral RNA
  • the initial stages of infecting the cell.

Interferons have four main actions. Click on the hotspots in the diagram below to learn more.

Complement protein system

The complement system is a group of more than 30 proteins that are made in the liver. They are released in an inactive form to circulate through the body’s vessels and tissues. Once they interact with a pathogen they become activated and work to complement the other actions of the immune system. They do this by:

  • helping to increase inflammation
  • recruiting phagocytes
  • enhancing opsonisation for phagocytes
  • directly attacking some pathogens by forming a membrane attack complex (MAC) to lyse (burst) pathogens.

Complement proteins also act on one another to activate various forms of complement proteins and to amplify how many complement proteins are activated. This is called a complement cascade and helps to increase the response and provide more rapid aid to the innate system cells.

Graphic representing the complement cascade. At the top is a single complement protein, represented as a blue circle, from this 3 arrows extend downwards to three more complement proteins. From these, arrows extend to more proteins. Over several rows, more and more complement proteins are added, each with an arrow coming from the complement proteins in the row above. There is text that reads”Each activated complement protein can activate other complement proteins, producing a complement cascade. This amplifies the impact of the complement proteins.

See more details about complement proteins and their actions by clicking on the hotspots in the image below.