An infection can be seen as a battle between the invading pathogens and the host. Our bodies are equipped to fight off invading microbes that may cause disease. These are called our natural defences.
The immune system is the term used to describe a system of many biological structures and processes within an organism that protects against disease.
To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism's own healthy tissue.
In many species, the immune system can be classified into subsystems, such as the innate immune system versus
the adaptive immune system.
Natural defence