Atlas of Veterinary Hematology || Leukocytes

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<ul><li><p>CHAPTER 3</p><p>Leukocytes</p><p> NEUTROPHIL MORPHOLOGY</p><p>Mammalian leukocytes, or white blood cells, have been classified as eitherpolymorphonuclear (PMN) or mononuclear leukocytes. The polymorphonuclearleukocytes have condensed, segmented nuclei. They are commonly referred toas granulocytes because they contain large numbers of cytoplasmic granules.The granules in these cells are lysosomes containing hydrolytic enzymes, anti-bacterial agents, and other compounds. Primary granules are synthesized in thecytoplasm of late myeloblasts or early promyelocytes. They appear reddishpurple when stained with routine blood stains such as Wright-Giemsa. Second-ary (specific) granules appear at the myelocyte stage of development in thebone marrow. Three types of granulocytes (neutrophils, eosinophils, and baso-phils) are identified by the staining characteristics of their secondary granules.</p><p>Normal Neutrophil MorphologyNormal neutrophil morphology is similar in common domestic mammalianspecies. The chromatin of the nucleus is condensed (dark-staining clumpedareas separated by lighter-staining areas) and segmented (lobulated) and stainsblue to purple (Fig. 15A). Nuclear lobes may be joined by fine filaments, butgenerally there is simply a narrowing of the nucleus between lobes without truefilament formation. When an area of the nucleus has a diameter less than two-thirds the diameter of any other area of the nucleus, the neutrophil is classifiedas mature, even if only two lobes are present (Fig. 15B). The nuclear outline ismore scalloped (jagged) in horses than in other species (Fig. 15C). The back-ground cytoplasm generally appears colorless but may appear pale pink orfaintly basophilic (Fig. 15D). Neutrophil granules either do not stain, or appearas light pink rods with routine blood stains. A Barr body (sex chromatin lobeor drumstick) is present in a low percentage of neutrophils from females (Figs.15E , 15F).1l This round, basophilic body is attached to the nucleus by a thinchromatin strand. It represents the pyknotic inactivated remains of one of thetwo X chromosomes.</p><p>45</p></li><li><p>FIGURE 15. See legend on opposite page.</p><p>46</p></li><li><p>Morphology of Left Shifts</p><p>CHAPTER 3 / LEUKOCYTES 47</p><p>Mature segmented neutrophils and, sometimes, low numbers of band neutro-phils are released from bone marrow into blood in normal animals. Whenincreased numbers of nonsegmented neutrophilic cells are present in blood,their presence is referred to as a left shift.</p><p>Band neutrophils are commonly seen in blood, with metamyelocytes andmyelocytes present less often and promyelocytes and myeloblasts rarely encoun-tered. Morphologic changes that occur as cells of the granulocytic series un-dergo maturation from myeloblasts to mature granulocytes in bone marrowinclude slight diminution in size, decrease in nucleus: cytoplasm (N: C) ratio,progressive nuclear condensation, changes in nuclear shape, and the appearanceof cytoplasmic granules. The background (i.e., nongranular) cytoplasm colorchanges from gray-blue in myeloblasts to nearly colorless in mature neutrophils,in the absence of toxicity. However, cytoplasmic toxicity is often present inanimals with pronounced left shifts in blood.</p><p>FIGURE 15. Neutrophils and their precursor cells. A. Neutrophil in blood from a dog.Wright-Giemsa stain. B. Bilobed neutrophil in blood from a cow. Wright-Giemsa stain. C. Twoneutrophils in blood from a horse. Wright-Giemsa stain. D. Neutrophil with slightlypink cytoplasm inblood from a cow. Wright-Giemsa stain. E. Neutrophil in blood from a female dog exhibiting a sexchromatin lobe or Barr body. Wright-Giemsa stain. F. Neutrophil in blood from a female catexhibiting a sex chromatin lobe or Barr body. Wright-Giemsa stain. G. Promyelocyte with purplecytoplasmic granules in blood from a dog with acute myelomonocytic leukemia (AML-M4). Wright-Giemsastain. H. Promyelocyte with faintly staining purple cytoplasmic granules in blood from a cat with amarked left shift (leukemoid reaction) secondary to a bacterial infection that resulted in the formation ofmultiple draining abscesses. Wright-Giemsa stain. I. Neutrophilic myelocyte in blood from a dog withchronic myeloid leukemia. Wright-Giemsa stain. J. Neutrophilic metamyelocyte in blood from a dogwith chronic myeloid leukemia. Wright-Giemsa stain. K. Band neutrophil in blood from a dog withimmune-mediated hemolytic anemia. Wright-Giemsa stain. L. S-shaped band neutrophil in bloodfrom a dog with immune-mediated hemolytic anemia. Wright-Giemsa stain. M. Neutrophil withfoamy basophilia (toxicity) of the cytoplasm in blood from a cat with septic peritonitis. Wright-Giemsastain. N. Neutrophil with doughnut-shaped nucleus and foamy basophilia (toxicity) of the cytoplasmin blood from a cat with septic peritonitis. Wright-Giemsa stain. O. Toxic metamyelocyte with foamybasophilia of the cytoplasm in blood from a cat with septic peritonitis. Wright-Giemsa stain. P. Toxicneutrophil with foamy basophilia and Dohle bodies (angular blue inclusions) in the cytoplasm in bloodfrom a cat with septic peritonitis. Wright-Giemsa stain. Q. Toxic neutrophil with foamy basophilia andDohle bodies in the cytoplasm in blood from a cat with a marked left shift (leukemoid reaction) secondaryto a bacterial infection that resulted in the formation of multiple draining abscesses. Wright-Giemsa stain.R. Band neutrophil with lightly basophilic cytoplasm containing Dohle bodies in blood from a horse.Wright-Giemsa stain. S. Toxic band neutrophil with foamy basophilia and Dohle bodies in thecytoplasm in blood from a cat with septic peritonitis. Wright-Giemsa stain. T. Toxic neutrophilicmetamyelocyte with foamy basophilia and faintly staining Dohle bodies in the cytoplasm in blood from acat with a marked left shift (leukemoid reaction) secondary to a bacterial infection that resulted in theformation of multiple draining abscesses. Wright-Giemsa stain. U. Dohle bodies in the cytoplasm oftwo neutrophils in blood from a cat, without other cytoplasmic evidence of toxicity. Wright-Giemsa stain.v. Band neutrophil with toxic granulation in blood from a horse with acute salmonellosis. Wright-Giemsastain. W. Band neutrophil with toxic granulation in blood from a Holstein cow with a bacterialinfection. Wright-Giemsa stain. X. Neutrophilic metamyelocyte with toxic granulation in blood from aHolstein cow with a bacterial infection. Wright-Giemsa stain.</p></li><li><p>48 SECTION I I BLOOD</p><p>FIGURE 16. Neutrophils and their precursor cells. A. Two toxic band neutrophils and a toxicneutrophilic metamyelocyte (bottom) with foamy basophilic cytoplasm in blood from a cat. The band onthe right appears to have a fragmented nuclear membrane forming a nuclear vesicle. Wright-Giemsa stain.B. Toxic left shift in the blood of a cat with a leukemoid reaction secondary to a bacterial infection thatresulted in the formation of multiple draining abscesses. Two neutrophilic cells have doughnut-shapednuclei. Wright-Giemsa stain. C. Giant neutrophil (bottom) in the blood of a cat with a leukemoid</p><p>(Continued)</p></li><li><p>CHAPTER 3 I LEUKOCYTES 49</p><p>Myeloblasts. The morphology of myeloblasts is described in the section onblast cells in blood (Fig. 24). Their presence indicates the likelihood of amyeloproliferative disorder.</p><p>Promyelocytes. Promyelocytes or progranulocytes have round to oval nucleiwith lacy to coarse chromatin. Although nucleoli or nucleolar rings may be seenin some promyelocytes, most exhibit no evidence of nucleolar structures. Theirmost identifiable characteristic is the presence of many magenta-staining pri-mary granules within light-blue cytoplasm (Figs. lSG, ISH).Myelocytes. Myelocytes have round nuclei (Fig. 151), but they are generallysmaller with more nuclear condensation and lighter-blue cytoplasm than pro-myelocytes. Primary, magenta-staining granules characteristic of promyelocytesare no longer visible in myelocytes. Secondary granules that characterize neutro-phils are present, but difficult to visualize because of their neutral-stainingcharacteristics.</p><p>Metamyelocytes. Nuclei with slight indentations are still classified as myelo-cytes, but once the nuclear indentation extends more than 25% into the nu-cleus, the cell is called a metamyelocyte (Fig. 1ST). Nuclear condensation be-comes readily apparent at this stage of maturation.</p><p>Band Cells. Cells with thinner, rod-shaped nuclei with parallel sides are calledbands (Fig. 15K). No area of the nucleus has a diameter less than two thirdsthe diameter of any other area of the nucleus. Band cell nuclei twist to conformto the space within the cytoplasm, and U-shaped or S-shaped nuclei (Fig. lSL)are common. Chromatin condensation is prominent, and the cytoplasm appear-ance is essentially the same as that seen in mature neutrophils. Once nuclearsegments form, the cell is called a mature neutrophil, even if only two lobes arepresent (Fig. lSB).</p><p>Disorders with Left ShiftsLeft shifts are usually associated with inflammatory conditions. These inflamma-tory conditions are often infectious but may be noninfectious, such as inimmune-mediated disorders and infiltrative marrow disease.':" Left shifts arealso present in animals with chronic myeloid leukemia and Pelger-Huet anomaly.</p><p>Inflammation. The presence of a significant left shift in animals with aninflammatory disorder indicates that the stimulus for release of neutrophilsfrom bone marrow is greater than can be accommodated by release from</p><p>reaction secondary to a bacterial infection that resulted in the formation of multiple draining abscesses.Wright-Giemsa stain. D. Left shift in the blood of a dog with chronic myeloid leukemia. Bandneutrophils, neutrophilic metamyelocytes, and a neutrophilic myelocyte are present. Wright-Giemsa stain.E. Band neutrophil (left) and neutrophilic myelocyte (right) in the blood of a dog with Pelger-Huetanomaly. Wright-Giemsa stain. F. Band neutrophil (left), bilobed neutrophil (center), and eosinophilicmyelocyte (right) in the blood of a cat with Pelger-Huet anomaly. Wright-Giemsa stain.</p></li><li><p>50 SECTION I / BLOOD</p><p>mature neutrophil stores alone. The magnitude of a left shift in response toinflammation can vary from slightly increased numbers of bands to severe leftshifts with metamyelocytes, myelocytes, and, rarely, even promyelocytes presentin blood. The total neutrophil count may be low, normal, or high, dependingon the number of these cells released from the bone marrow versus the numberutilized in the inflammatory process. Toxic cytoplasm is often present in ani-mals with left shifts in response to inflammatory disorders (Fig. 16A). Otherabnormalities that may be present include donut-shaped nuclei and giant neu-trophils (Figs. 16B, 16C).</p><p>A marked leukocytosis (total leukocyte count of 50,000 to 100,000/JLL)with a marked left shift back to at least myelocytes associated with an inflam-matory condition is called a leukemoid reaction, because it resembles the bloodpattern seen in chronic myeloid leukemia. Left shifts associated with leukemoidreactions are usually orderly, with mature segmented neutrophils being themost numerous neutrophilic cells present, bands being the next most numer-ous, metamyelocytes being less numerous, and myelocytes being present in lownumbers. When a leukemoid response is present, a localized purulent inflam-matory condition such as pyometra is suspected.Chronic Myeloid Leukemia. Chronic myeloid leukemia (CML) presents with ahigh total leukocyte count (usually greater than 50,000/ILL) with marked neu-trophilic left shift in blood (Fig. 16D),l30-132 In domestic animals, CML isprimarily seen in dogs. Increased numbers of monocytes, eosinophils, and/orbasophils may also be present. Myeloblasts are either absent or present in lownumbers in blood. CML is suspected when no inflammatory disorder can befound to explain the extreme left shift. The left shift present in CML is usuallyless orderly than those seen in leukemoid reactions. The presence of dysplasticabnormalities in other blood cell types also supports a diagnosis of CML. Onthe other hand, the presence of moderate to marked cytoplasmic toxicity,increased inflammatory plasma proteins, and physical evidence of inflammationsuggest a leukemoid reaction is present, rather than CML.Pelger-Huet Anomaly. The term hyposegmentation refers to a left shift withcondensed nuclear chromatin without nuclear constrictions (Figs. 16E, 16F). Itoccurs as an inherited trait in the Pelger-Huet anomaly in dogs and cats.133,134Eosinophils and basophils may also be affected. No clinical signs are associatedwith animals that are heterozygous for this disorder. A pseudo-Pelger-Huetanomaly may occur transiently with chronic infections and rarely following theadministration of certain drugs or in animals with myeloproliferative disor-ders.!"</p><p>Toxic CytoplasmWhen the cytoplasm of a neutrophilic cell has increased basophilia, has foamyvacuolation, and/or contains Dahle bodies, it is said to be toxic. These morpho-logic abnormalities develop in neutrophilic cells within the bone marrow priorto their release into the circulation.135,136</p></li><li><p>CHAPTER 3 / LEUKOCYTES 51</p><p>Foamy Basophilia. Foamy basophilia often occurs with severe bacterial infec-tions but can occur with other causes of toxemia (Figs. 15M-1ST). Whenviewed by electron microscopy, foamy vacuolation appears as irregular, elec-tron-lucent areas that are not membrane bound. Cytoplasmic basophilia resultsfrom the persistence of large amounts of rough endoplasmic reticulum andpolyribosomes.l"</p><p>Dohle Bodies. Dohle bodies are bluish, angular cytoplasmic inclusions of neu-trophils and their precursors (Figs. 15P-15U). They are composed of retainedaggregates of rough endoplasmic reticulum." By themselves, these inclusionsrepresent mild evidence of toxicity and are sometimes seen in neutrophils ofcats that do not exhibit signs of illness (Fig. 15U). Dohle bodies must bedifferentiated from iron-positive granules, distemper inclusions in dogs, andgranules present in neutrophils from cats with inherited Chediak-Higashi syn-drome.</p><p>Toxic Granulation. Toxic granulation refers to the presence of magenta-stain-ing cytoplasmic granules (Figs. 15V-15X, 17A).52 These granules consist ofprimary granules that have retained the staining intensity normally observed inpromyelocytes in the bone marrow. The presence of toxic granulation andcytoplasmic basophilia suggests severe toxemia. Toxic granulation may be seenin horses, cattle, and sheep but is rarely seen in dogs and cats. Toxic granula-tion should not be confused with the pink staining of secondary granules whichis not a sign of toxicity. Toxic granulation must be differentiated from thegranules present in some Birman cats, granules in animals with certain lysoso-mal storage disorders, and miscellaneous granules and inclusions to be dis-cussed subsequently.</p><p>Granules and InclusionsNormal Foals. Purple granules are often seen in neutrophils from foals with-out other evidence of cytoplasmic toxicity (Fig. 17B),109 the clinical significanceof which is unclear. It is assumed that, like toxic g...</p></li></ul>


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