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[[Image:Heterophil.jpg|150px|thumb|right|'''Heterophil''' (Copyright © RVC. All rights reserved)]]
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==Introduction==
[[Image:Heterophil.jpg|150px|thumb|right|'''Heterophil''' (Copyright © RVC)]]
Heterophils are the most abundant '''granulocyte''' in most '''avian species''' and occur alongside [[lymphocytes]], [[monocytes]], [[eosinophils]] and [[basophils]] in avian blood. These cells are also found in some '''reptile and mammalian species'''.
Heterophils are large cells with a round to lobed nucleus and fusiform acidophilic cytoplasmic granules. The size varies between species and often varies in individual blood smears. The primary function of heterophils may be phagocytosis. In some species heterophils are the most common [[Leucocytes|leucocyte]].[[Category:Lizard_and_Snake_Glossary]]
==Development==
Heterophils have a similar development to other granulocytes; this process is called [[Leukopoiesis#Granulopoiesis|granulopoiesis]].
==Appearance==
The cytoplasm of normal heterophils appears '''colourless''' and contains '''eosinophilic granules''' (dark orange to brown-red) with Romanowsky stains. The cytoplasmic granules are elongated (rod or spiculated shape) but they may appear oval to round in some species.
The granules frequently have a distinct central body that appears to be refractile. The granules may be affected by the staining process and appear atypical.
The nucleus of mature heterophils is '''lobed''' (usually two to three) with coarse, clumped chromatin that stains purple. The nucleus is often partially hidden by the cytoplasmic granules.
==Function==
Heterophils are functionally '''equivalent to [[Neutrophils|neutrophils]]'''. They actively participate in '''inflammatory lesions''' and are '''phagocytic'''.
The cytoplasmic granules of heterophils contain lysozyme and proteins needed for bactericidal activity, although chicken heterophils lack peroxydase activity.
==Changes==
===Immature Heterophils===
These have '''increased cytoplasmic basophilia''', '''non-segmented nuclei''' and '''immature granules''' compared with normal, mature heterophils.
The immature heterocytes most frequently encountered in blood are '''myelocytes and metamyelocytes'''. Myelocytes are larger than mature heterophils and they have a blue cytoplasm as well as secondary, rod-shaped granules and a round to oval non-segmented nucleus. Metamyelocytes resemble myelocytes except that the nucleus is indented and the rod-shaped granules occupy more than half the cytoplasmic space.
'''Band heterophils''' resemble mature heterophils, except that the nucleus is not lobed. The nucleus is often hidden behind the cytoplasmic granules, and it can be difficult to identify a band heterophil. Special stains can help with this.
===Toxic Heterophils===
Heterophils exhibit '''toxic changes in response to severe systemic illness'''.
These changes are quantified as to the number of toxic cells and the severity of the toxicity.
Toxic heterophils have '''increased cytoplasmic basophilia, vacuolisation, abnormal granulation (degranulation, deeply basophilic granules, coalescing granules) and degeneration of the cell nucleus'''.
The degree of toxicity can be rated on a '''scale''' of 1+ to 4+:
:1+ toxicity: heterophils exhibit increased cytoplasmic basophilia
:2+ toxicity: heterophils have deeper cytoplasmic basophilia and partial degranulation
:3+ toxicity: heterophils have deep cytoplasmic basophilia, moderate degranulation, abnormal granules and cytoplasmic vacuolisation
:4+ toxicity: heterophils have deep cytoplasmic basophilia, moderate to marked degranulation with abnormal granules, cytoplasmic vacuolisation and karyorrhexis or karyolysis.
The number of toxic heterophils is graded as few (5-10%), moderate (11-30%) or marked (>30%).
{{Learning
|flashcards = [[Avian Medicine Q&A 21]]<br>[[Reptiles and Amphibians Q&A 11]]
}}
==References==
Thrall, M. (2004) '''Veterinary haematology and clinical chemistry''' ''Wiley-Blackwell''
Fudge, A. (2000) '''Laboratory medicine: avian and exotic pets''' ''Elsevier Health Sciences''
Feldman, B. (2000) '''Schalm's Veterinary haematology''' ''Wiley-Blackwell''
Frye, FL & Williams, DL (1995) '''Self-Assessment Colour Review - Reptiles & Amphibians''' ''Manson''
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