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Eosinophils are a similar size to [[Neutrophils|neutrophils]], have a bilobed nucleus and are characterised by the large eosinophilic granules present in their cytoplasm. Produced in the [[Bone Marrow - Anatomy & Physiology|bone marrow]] they migrate into circulation briefly before moving into tissue where they survive for around six hours. The proportion of eosinophils circulating depends on the state of the animal. Normally numbers are very low but will rise considerably during a parasitic infection or allergic reaction.
Eosinophils are a similar size to [[Neutrophils|neutrophils]], have a bilobed nucleus and are characterised by the large eosinophilic granules present in their cytoplasm. Produced in the [[Bone Marrow - Anatomy & Physiology|bone marrow]] they migrate into circulation briefly before moving into tissue where they survive for around six hours. The proportion of eosinophils circulating depends on the state of the animal. Normally numbers are very low but will rise considerably during a parasitic infection or allergic reaction.
Eosinophils are mainly located in connective tissue associated with routes into the animal i.e. the respiratory, alimentary, and urogential systems. They play key roles in reacting to [[Parasites|parasites]] and allergens but have limited phagocytic ability and therefore play no role in bacterial infections.
Eosinophils are mainly located in connective tissue associated with routes into the animal i.e. the respiratory, alimentary, and urogenital systems. They play key roles in reacting to [[Parasites|parasites]] and allergens but have limited phagocytic ability and therefore play no role in bacterial infections.
== Development ==
== Development ==
Eosinophils are involved in [[Type I Hypersensitivity|type I hypersensitivity]] reactions.
Eosinophils are involved in [[Type I Hypersensitivity|type I hypersensitivity]] reactions.
In an infection or allergic reaction, eosinophil numbers are increased by the release of [[Leukopoiesis#Eosinophils|Il-3, Il-5 and GM-CSF]] by Th2 and [[Mast Cells|mast cells]]. This causes more eosinophils to be released into the blood stream. The eosinophils are then attracted to the required site of action by chemicals known as eotaxins which are released by mast cells. Histamine and its breakdown products also act as attractants. These same products activate the eosinophil increasing its affinity to bind to [[IgE]].
In an infection or allergic reaction, eosinophil numbers are increased by the release of [[Leukopoiesis#Eosinophils|IL-3, IL-5 and GM-CSF]] by T<sub>H</sub>2 and [[Mast Cells|mast cells]]. This causes more eosinophils to be released into the blood stream. The eosinophils are then attracted to the required site of action by chemicals known as eotaxins which are released by mast cells. Histamine and its breakdown products also act as attractants. These same products activate the eosinophil increasing its affinity to bind to [[IgE]].
Large numbers of eosinophils in a tissue give the tissue a greenish colour.
Large numbers of eosinophils in a tissue give the tissue a greenish colour.
=== Anti-parasitic ===
=== Anti-parasitic ===
Fc receptors on eosinophils allow them bind to [[Parasites|parasites]] coated in antibodies and once bound they degranulate. The specific granules release EDN which interferes with the parasitic nervous system while MBP, ECP and EPO (EPO dissolves the carbohydrate coat of the parasite) all have anthelmintic and anti-[[Protozoa|protozoal]] actions. These proteins act as stimulants to mast cells causing them to release histamine and thus attracting more eosinophils. However, they also damage the animal’s tissue as well as the [[Parasites|parasites]].
=== Allergic ===
=== Allergic ===