Two systems working together

The immune response of an animal is built from two cooperating systems:

• Innate (natural, non-specific) immunity – present from birth, reacts quickly, and treats all invaders in broadly the same way.
• Acquired (adaptive, specific) immunity – develops during life after contact with a particular pathogen, is aimed at that one pathogen, and leaves a memory.

• These two systems are not rivals.
• The innate system is needed for the acquired one to start properly (for example, phagocytes of the innate system pick up and display pieces of the invader that the acquired system then recognises), and the acquired system in turn boosts the innate one (for example, antibodies mark microbes for engulfment).
• Each activates the other, so the body copes successfully only when both are working.