The main function of white blood cells is to help protect the human body from infection as well as other foreign materials. White blood cells are also known as leukocytes, and they develop in bone marrow from stem cells.
There are five different types of white blood cells, including neutrophils, lymphocytes, monocytes, eosinophils and basophils. The lack of white blood cells, or the incidence of too many can cause serious disorders in the body. Disorders are more common regarding neutrophils and lymphocytes. A common disorder from a lack of white blood cells is called leukopenia. The presence of leukopenia can make a person much more susceptible to infections and contagious diseases.