The immediate response to infection – the innate immune system.

The term ‘innate immune system’ is used to describe pre-existing defence mechanisms that are designed to prevent infection by pathogens or to mount an immediate defence against the infectious agent. The physical, chemical and biochemical barriers to infection are part of the innate immune system. They are called ‘innate’ or ‘natural’ because they are present before infection, although the amount of some components may increase following infection.