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If an antigen injures tissue cells, chemical substances are released which initiate and perpetuate the inflammatory reaction. Leukotaxine increases capillary permeability and, by chemotaxis, it attracts neutrophils into the area of injured cells.
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A leukocytosis-promoting factor, also produced from injured cells, is carried by the blood stream to the bone marrow where it stimulates granulopoiesis, thereby increasing the supply of neutrophils. In development of a severe inflammatory response, the need for neutrophils in large numbers is immediate.
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A neutrophil maturation and storage pool" exists in the bone marrow to meet the initial demand, whereas production of new neutrophils requires two to three days from the time of initial stimulus.
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Mature neutrophils are preferentially released over band cells from the maturation and storage pool into the peripheral blood. When the need for neutrophils exceeds the ability of bone marrow to supply that need in the form of mature neutrophils, then immature forms (band, metamyelocytes, etc.) are released to peripheral blood. Thus, the intensity of a disease process may be gauged by the extent of the shift to the left.
CLASSIFICATION OF THE RESPONSES OF LEUKOCYTE
The ability of the bone marrow to respond to a bacterial infection is measured by the magnitude of the total leukocyte count; the intensity of the response is gauged by the extent of the left shift.
REGENERATIVE LEFT SHIFT
Characterized by a leukocytosis due to a neutrophilia with the appearance of immature granulocytes in peripheral blood.
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A slight left shift is limited to the occurrence of band neutrophils.
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A moderate left shift includes both band and metamyelocytes.
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A marked left shift includes myelocytes and progranulocytes.
DEGENERATIVE LEFT SHIFT
The total leukocyte count remains in the normal range or is only slightly elevated, while the immature granulocytes are markedly increased.
LEUKOMOID BLOOD PICTURE
Similar to a regenerative left shift except the total white count is extremely elevated suggesting a granulocytic leukemia.
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The process stimulating the count is other than leukemia.
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A leukemoid hemogram may be seen in pyometra of the dog, abscess formation, severe hemorrhage or hemolytic crisis.
TOXIC CHANGES IN NEUTROPHILS
The severity of the infection is measured by the occurrence of toxic changes in the neutrophils. The following are recognized as manifestations of toxicity:
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Diffuse basophilia of the cytoplasm or foamy blue cytoplasm may be seen in all domestic animals with extreme toxicity.
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Diffuse basophilia, bizarre giant neutrophils and formation of Dohle bodies in the cytoplasm are commonly observed in the neutrophils of the cat in toxemic diseases.
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In the dog, the occurrence of vacuoles located along the periphery of the cell so as to suggest a moth-eaten appearance.
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The occurrence of blue-black or large reddish granules in the cytoplasm ("toxic granulation") of neutrophils in the sheep, cow, horse dog and cat.
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