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'''White blood cells''' are a component of [[blood]]. As part of the body's [[immune system]], their function is to protect the body from disease and infection. White blood cells come in several varieties, each with a different role to play in neutralizing harmful foreign substances. White blood cells, like all [[blood cells]], are produced in the [[bone]] marrow.  

'''White blood cells''' are a component of [[blood]]. As part of the body's [[immune system]], their function is to protect the body from disease and infection if pathogens get in the bloodstream. White blood cells come in several varieties, each with a different role to play in neutralizing harmful foreign substances. White blood cells, like all [[blood cells]], are produced in the [[bone]] marrow.  

They are also known as leukocytes. There are five main types of leukocytes, and these types are produced from immature cells in the [[lymphatic system]] in response to the body's needs. For example, infection with bacteria will cause more [[macrophage]]s to be produced and fewer NK cells, in response to "alarm signals" called [[chemokine]]s. Macrophages then exit the bloodstream, migrate towards the site of infection, and attempt to neutralize the invading pathogens. Others begin producing antibodies or recruit other systems to help.  

They are also known as leukocytes. There are five main types of leukocytes, and these types are produced from immature cells in the [[lymphatic system]] in response to the body's needs. For example, infection with bacteria will cause more [[macrophage]]s to be produced and fewer NK cells, in response to "alarm signals" called [[chemokine]]s. Macrophages then exit the bloodstream, migrate towards the site of infection, and attempt to neutralize the invading pathogens. Others begin producing antibodies or recruit other systems to help.