Eosinophils play a significant role in the response to infection with parasites and allergens.  Similar to neutrophils in that eosinophils can eat pathogens whole and then destroy them with internal granules.  If the pathogen is too big to swallow whole, the eosinophil will release chemical grenades.  They patrol the bloodstream until called into action by other immune cells.

Description:   A white blood cell that is part of the innate immune system.

Location:  Most often, they are found in the bone marrow and circulating in blood stream.  However, they will quickly travel to the site of a potential parasite or allergen infection.

Weapons:  Internal granules - digest eaten pathogens.  Chemical grenades - chemicals that can be released to kill large pathogens.

Appearance:  12-17 micrometers in height, contain a single large nucleus and dark granules.
Source: arise from stem cells in the bone marrow.

Life span:  8-12 days.  Spends a few hours in the bloodstream, and then migrates to skin or mucous membranes

Number: Around 7-16 billion in an average adult, however this number can rise quickly to fight infection by parasites or allergens.