Neutrophils
comprise 60-70% of all leukocytes in the blood.
Neutrophils arise from precursors in the bone marrow and have a
half-life of 4-8 hours in the blood and about a day of life in
the tissues. Neutrophils hasten to inflammatory sites. They are
mobile cells and can pass through capillaries and engulf bacteria
by phagocytosis. Neutrophils secrete a fever inducing agent
called pyrogen which also helps the body fight infection.
Eosinophils are
named by virtue of the fact that the
granules of cytoplasm are stainable with acid dyes, such as
eosin. These cells are present in small numbers (2-4% of the
blood), but under certain pathological conditions they show a
marked increase. The exact function of eosinophils has been a
mystery for many years.
Basophils are
formed in the bone marrow and have a
polymorphic nucleus. They occur only to the extent of about 1% of
the leukocytes. The function of these cells is poorly understood.
They are known to play a role in immediate hypersensitivity
reactions and in some cell-mediated delayed reactions, such as
contact hypersensitivity in humans, skin graft or tumor
rejections and hypersensitivity to certain microorganisms in
animals.