Immune system

The immune system has a difficult job: It is a 24-hours-a-day, 7-days-a-week battle against a well-equipped and persistent army of numerous pathogens living in the environment such as viruses, bacteria, fungi, and parasites (e.g. malaria pathogens). The immune system also removes harmful substances, that enter the body through food or by breathing, and destroys developing cancer cells.
The white blood corpuscles play an important role in these defense mechanisms.