ALTERED LEUKOCYTE MORPHOLOGY AND FUNCTION

11 ALTERED LEUKOCYTE MORPHOLOGY AND FUNCTION



Stephen D. Gaunt



1 What are reactive lymphocytes, or immunocytes?


Immunocytes are large-sized lymphocytes with intensely basophilic cytoplasm and occasionally a prominent nucleolus that appear similar to lymphoblasts. These cells may be more similar to plasma cells, with a clear Golgi area in basophilic cytoplasm, an eccentric nucleus, and even cytoplasmic inclusions (Russell bodies). These cells occur in low numbers, with most of the lymphocytes appearing normal. These reactive lymphocytes are observed in animals undergoing immune response, typically during infectious inflammatory diseases or after vaccination. The low number of these cells and the clinical history provide the convincing evidence that these lymphocytes are antigenically stimulated, not neoplastic (Figure 11-1).


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Figure 11-1 Reactive lymphocyte (immunocyte) from a cat. (Wright’s stain; 330×.)



2 What are toxic changes in neutrophils?


Cytoplasmic changes occur in blood neutrophils during intense inflammation from many causes (infectious or noninfectious). The toxic changes observed in neutrophils include Döhle bodies, diffuse cytoplasmic basophilia, cytoplasmic (“foamy”) vacuolization, and infrequently, toxic granulation (Figure 11-2). Döhle bodies are small (1-2 μ), lightly basophilic inclusions that occur in low numbers near the periphery of cytoplasm. Döhle bodies may also occur in low numbers of neutrophils in healthy cats.


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Figure 11-2 Band neutrophil with Döhle bodies, cytoplasmic basophilia, and cytoplasmic vacuolization. (Wright’s stain; 330×.)



3 What causes the formation of toxic changes in neutrophils?


These changes first appear in early neutrophil precursors in the marrow as a developmental abnormality and are not induced in mature neutrophils by “toxins.” For example, Döhle bodies and the cytoplasmic basophilia are rough endoplasmic reticulum and free ribosomes, respectively, that normally disappear in early neutrophil precursors. The cytoplasmic vacuolization results from disruption of cytoplasmic granules in neutrophilic precursors. Toxic changes apparently result from the heightened and quickened pace of granulopoiesis during particularly intense inflammatory responses.



4 How are toxic changes reported by laboratories?


Any toxic change(s) observed in blood neutrophils should be included in the “leukocyte morphology” comments on the complete blood count (CBC). Different toxic changes may occur individually, in various combinations, and in varying degrees between neutrophils. Because of this variability in occurrence and the lack of clinical correlation, grading systems for toxic changes are not used in most laboratories.



5 What causes abnormal granulation in neutrophils?


The rare reports of increased prominence of azurophilic granules in neutrophils and other granulocytes (especially basophils) and monocytes include the following:


a. Observed in some normal foals and Birman cats

b. Occur in inflammatory diseases as a toxic change

c. Chediak-Higashi syndrome in cattle and Persian cats (abnormal fusion of granules)

d. Lysosomal storage diseases (mucopolysaccharidosis in dogs and cats, Figure 11-3)

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Figure 11-3 Neutrophils with prominent cytoplasmic granules in a young dog with mucopolysaccharidosis, MPS VII. (Wright’s stain; 330×.)



6 What is the significance of giant neutrophils?


Segmented neutrophils that are up to twice the size of normal neutrophils, but with otherwise unremarkable morphology, are rarely observed on blood smears. This finding indicates dysgranulopoiesis, in which a mitotic cell division was likely skipped by an early precursor and larger neutrophils resulted. Giant neutrophils occur with inflammatory diseases and in cats with feline leukemia virus (FeLV) infection (Figure 11-4).


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Figure 11-4 Blood smear from a dog with giant and normal-sized neutrophils. (Wright’s stain; 330×.)

Related posts:

  1. ERYTHROCYTE DISORDERS
  2. OVERVIEW: HEMOSTATIC COMPONENTS AND DISORDERS
  3. INTERPRETATION OF THE LEUKOGRAM
  4. AVIAN BIOCHEMICAL ANALYSIS

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Aug 26, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on ALTERED LEUKOCYTE MORPHOLOGY AND FUNCTION

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