Cell Types Flashcards
Erythrocyte, or “red blood cell” (RBC). Despite the common term, this is not a cell at all, although it’s derived from true cells. The RBC is the mature stage of development of a cell line in which the nucleus (present in earlier forms) has been lost.
erithrocytes (red) with platelets (purple)
Platelets are little bitty things, only 2 to 4 microns in diameter (about half the size of an RBC), and round to oval in shape. They have a central zone that is slightly basophilic, and a pale, homogeneous periphery. Look for them in the spaces between erythrocytes. The image above shows platelets in a smear: they appear as small fragments with a blue cast to them. They’re much smaller than the erythrocytes: maybe 1-3 microns. The scanning electron micrograph at the right is of a group of platelets which have begun to initiate a clot. The stringy material covering them is fibrin, the matured, insoluble fibrillar component of blood.
segmented neutrophil
Neutrophils are the most common form of leukocyte in primates, dogs, cats, and horses. They have other names, frequently encountered in clinical literature: “polys” or “PMNs” are most common, both abbreviations for “polymorphonuclear leukocyte.” These cells can be identified on a smear by their size (about 9 to 12 microns diameter) and their characteristically segmented or lobulated nucleus. The nucleus in its mature form may have 3 to 5 lobes, connected together with fine threads of nuclear material. The granules in the cytoplasm are usually lightly stained, and may appear to be pink to purple. This variability of staining has resulted in the name “heterophil” being applied to these cells.
Neutrophil
The one in the smear shown here is from a monkey. Specifically, a female monkey. The extensive lobulation of the nucleus has produced a drumstick shape lobe, a “Barr Body” (named for Murray L. Barr, 1908-1995, a Canadian anatomist) which represents the extra X chromosome in females.
Eosinophils are much less common than neutrophils. They’re the same size or even slightly larger (10 to 14 microns) and their cytoplasmic granules are strongly eosinophilic, staining a bright orange-pink color. Typically the nucleus is bi-lobed, not multi-lobed as in the neutrophils. There’s some species variation in eosinophils. The granules are exceptionally large in horses (slide 1006) and it would be worth your while to compare the “typical” eosinophils from dogs and cats with those of the horse. Their function isn’t completely understood, but it’s known that eosinophils are involved in allergic responses.
Like the granules of neutrophils, the eosinophil’s granules contain lytic enzymes, but they’re much larger than those of neutrophils, and they stain pinkish red in Wright’s smears. The staining reaction is the most characteristic means of identifying these cells.
Another useful clue is the nuclear morphology. Eosinophils never show the extensive nuclear lobulation typical of the neutrophil, but typically have a bi-lobed nucleus. Because the granules can be so prominent, the lobation of the nucleus can sometimes be difficult to see
eosinophil
Basophils are by far the rarest of the granulocytes, and are believed to be absent from cats, rats, and mice. In fact, in all species the basophil the rarest of all of the formed elements. Once seen, they’re hard to mistake for any other cell type: in smears they have a deep purple, wine colored look to them, and the granules appear to be on the “outside” of the cell. They aren’t, of course, like any granules they’re intracellular. But the large granules in this rather small cell protrude considerably and stretch the plasma membrane. It sometimes looks as if the basophil had been coated with something and “rolled” in granules. The density of the staining is usually such as to obscure the nucleus, but when it’s visible it usually is S-shaped.
basophil
The lymphocyte is typically the most numerous and most important of the agranulocytes. Lymphocytes come in several sizes, those in the blood being characterized as “small” (5 to 10 microns) or “medium” types (10 to 18 microns). The “large” size is usually found outside the circulation, mostly in lymphatic organs. Lymphocytes can be identified in smears by their very high ratio of nucleus to cytoplasm. The nucleus is very densely stained, and usually round (although it may have a very slight indentation). The cytoplasm is a thin band to one side of the nucleus, and is stained a dusky blue color.
Erythrocyte Morphology
Normal Biconcave disc, dependent on species Most mature mammalian RBCs contain no nucleus
Poikilocytosis
variation in shape
Spherocytes
appear smaller and more dense due to spherical shape – may indicate immune-mediated anemia
Acanthocytes
red cells with several unevenly distributed surface projections, often with knobby ends – may be noted in spleen/liver disorders
Schistocytes
irregular RBC fragments resulting from trauma in circulation
Echinocytes or Crenation
several blunt or pointed evenly spaced surface projections. Usually an artifact of smear technique or age of blood.
Rouleaux
stacking of RBCs; may be associated with immune-mediated disease
lymphocyte
Monocytes are the second type of agranulocyte, and the largest of the circulating formed elements. A healthy monocyte will run anywhere from 16 to 25 microns in diameter, much larger than any other formed element. The nucleus varies in form, and may be kidney shaped, bean shaped, or (classically) horseshoe shaped, with a deep indentation.
The nuclear material of monocytes doesn’t stain as deeply as that of lymphocytes, and chromatin strands can be made out (at least one author has described it—in a remarkably colorful phrase—as a “spaghetti and meatball” nuclear pattern). The ratio of nuclear material to cytoplasm is also less than in the lymphocyte. The cytoplasm of the monocyte will stain a blue-gray color and is said to have a “ground glass” appearance due to the presence of fine granules in it.
Monocytes aren’t common in circulating blood, representing perhaps 5% to 8% of all leukocytes, but you do run across one now and then. When you do spot one, it’s pretty obvious what it is, based on the size alone. In addition, the greater amount of cytoplasm and the deeply indented nucleus (depending on the geometry of the section this may or may not be visible) are confirmation. In the image shown here, the monocyte is by far the largest cell in the field. The indentation of the nucleus isn’t pronounced, thanks to the orientation of the cell with respect to the plane of section, but the very significant amount of cytoplasm visible is: no lymphocyte would have as much. the slate-blue color of the cytoplasm is another clue. This cell is easily three times the size of the erythrocytes that are located near it. This cell was spotted on a slide of the liver, in one of the blood sinusoids; a good place to go hunting for circulating leukocytes.
Be aware that there’s a bit of a size overlap between large lymphocytes and small monocytes. Distinguishing which is which can take some practice and a sharp eye for details like nuclear configuration and colors. The best rule to use is that if you aren’t sure it’s a monocyte….it probably isn’t.
monocyte
The blood of non-mammals is somewhat different: the most conspicuous difference is that all non-mammals have nucleated erythrocytes. The presence of nuclei in mammalian erythrocytes is a sign of pathology, but in non-mammals it’s normal. In this case, the Greek root kytos (for “cell”) has real meaning, because in all non-mammals, the erythrocyte of the circulation is a true cell, complete with nucleus. As in mammals, its function is to carry oxygen to the tissues.
You’ll most commonly encounter non-mammalian blood in the form of avian blood. Avian erythrocytes (and non-mammalian ones in general) are oval in shape, and have a distinct centrally located nucleus. Although size varies somewhat with sex and breed, avian erythrocytes are typically about 6.0-8.0 µ wide and 9.0-12 µ long. The nucleus is strongly basophilic and the cytoplasm eosinophilic. Frequently you will be able to make out a clear area around the nucleus; this is an enlarged perinuclear space. The space is real—it’s present in all nucleated cells—but its enlargement to the point where it can be seen in a light microscope is probably a preparation artifact.
The thrombocyte, also seen in this field from slide 642, is the non-mammalian equivalent of the platelet, and it has the same function of on-the-spot repair of breaks in the vascular system. In some clinical contexts the word “thrombocyte” is used interchangeably with “platelet” in mammals, which strictly speaking isn’t correct usage. In birds, however, it is: the thromobocyte is a true cell, complete with nucleus and other organelles.
Thrombocytes are smaller than erythrocyte and in smears have a faintly bluish tinge to their cytoplasm. One immediately recognizable feature in good preparations is a small eosinophilic vacuole located at one end of the nucleus. It appears as an orange dot in most preparations. This perinuclear “dot” is part of the Golgi appar
blood cell lineage
monocyte species differences
Monocytes are extremely variable in appearance but there are no consistent species differences. Each of the four monocytes shown here as examples are from different species lymphs but all could be found in blood of any individual animal of any species. For example, the canine monocyte shown here would feel equally at home in a smear of horse blood and the cat monocyte could have been in dog blood.
Some monocytes resemble band or segmented neutrophils, as illustrated by the canine moncyte, while others, like this equine monocyte, may be mistaken for lymphocytes. In general, monocytes are recognized as cells that have abundant light to deep blue cytoplasm and nuclei that are not round. Chromatin is reticular or only slightly condensed. Most are larger than neighboring neutrophils and lymphocytes. Small pink granules are visible in some monocytes and many monocytes have several small discrete vacuoles. Nuclear shape amongst monocytes ranges from ameboid to bean-shaped to band-like to almost segmented. The texture of cytoplasm in a monocyte is slightly grainy or coarse compared to lymphocyte cytoplasm, which is very smooth and glassy.
left shift
In some animals, immature neutrophils may be seen in peripheral blood. The presence of immature neutrophils in blood is called a left shift. The most common cause of a left shift is inflammation (inflammatory cytokines stimulate both neutrophil production and release of mature and immature forms from the bone marrow), however immature neutrophils can also be released prematurely in bone marrow disorders, such as leukemia or severe marrow injury.
Immature neutrophils are classified based on their stage of maturation. The earliest identifiable neutrophil precursor is a myelocyte, which differentiates into a metamyelocyte, then a band neutrophil, and finally to a mature segmented neutrophil. Only the myelocyte is capable of division - all the more mature stages (metamyelocyte, band, segmented neutrophil) are incapable of division (post-mitotic). The primary criterion for differentiating immature neutrophils from each other is the shape of their nucleus, which starts to indent or constrict as the cell matures. A myelocyte has a round nucleus, a metamyelocyte has an indented or kidney-bean shaped nucleus and a band has a horse-shoe or parallel-sided shaped nucleus (see image below).
When performing a differntial cell count, we classify neutrophils into the “SEGMENTED” category if the nucleus has regions that are distinctly constricted (more than 50% of the width of the nucleus) or has lateral protrusions resulting in irregular nuclear margins. A cell whose nuclear margins are smooth and parallel (or nearly parallel) is a band neutrophil and should be counted as such. More immature stages are classified by their nuclear shape, as described above. Note that cells between these well-defined stages will always be seen in blood. Under these circumstances, the cell in question will be placed in the more mature category, i.e. a cell with nuclear features halfway between a band and a segmented neutrophil will be called a segmented neutrophil. More immature neutrophils can be counted separately as their specific categories or grouped together as “BAND” neutrophils. At Cornell University, all immature neutrophils (band neutrophils, metamyelocytes and myelocytes) are grouped into the “BAND” category of our differential cell count. Using the image above as an example, the cells B through D would be counted as “BANDS” and only cell A would be counted as a “SEGMENTED” neutrophil. However, if we observe stages that are less mature than a band neutrophil (metamyelocyte or myelocyte), we provide this information in the results. The presence of these more immature stages usually indicates more severe inflammation than the presence of band neutrophils alone. Again, the presence of band or more immature neutrophils in blood is called a left shift and usually indicates an inflammatory leukogram. Note that for a left shift, the band neutrophil count must be higher than the established reference interval for that species, but in general, most animals have very few to no band neutrophils normally in the circulation (some healthy dogs can have low numbers of band neutrophils in their blood). A degenerative left shift is the term used when the absolute numbers of band or immature neutrophils are greater than the absolute numbers of mature or segmented neutrophils. A degenerative left shift indicates severe inflammation, which is usually due to bacterial infection.
A common and important morphologic abnormality of neutrophils is so-called “toxic change”. This abnormality occurs when neutrophil maturation in the bone marrow is accelerated, usually as a response to inflammatory cytokines. Thus, a left shift and toxic change indicate an inflammatory leukogram and are usually (but not always) seen together.
This compilation of images is from a cow with severe inflammation secondary to an acute metritis and peritonitis. The cow had a degenerative left shift (more immature than mature neutrophils were counted). These images represent the different stages of neutrophil maturation: A: Mature segmented neutrophil; B: Band neutrophil; C: Neutrophilic metamyelocyte; D: Neutrophilic myelocyte. Note that the immature neutrophils are also demonstrating moderate toxic change - they have cytoplasmic baasophilia and cytoplasmic vacuolation.
lymphocyte species differences
Most of the lymphocytes that circulate in healthy dogs, cats, and horses are small (mature) cells that have round nuclei with smooth, dense chromatin and a small rim of lymphs blue cytoplasm. These are sometimes confused with nucleated RBCs. Some lymphocytes, as illustrated by the equine lymphocyte, are slightly larger and have a finer, looser chromatin pattern. The lymphocytes found in blood of normal ruminants are quite variable in appearance. Many are large lymphocytes, as shown in the right middle panel, with loosely clumped chromatin and fairly abundant cytoplasm.
So-called “reactive” lymphocytes are larger cells with coarse (mature) chromatin, and deep blue cytoplasm as shown in the bottom left panel. Lymphocytes with these characteristics are sometimes called immunocytes and are associated with an immune response. These are fairly common in blood of young animals, especially ones that have been recently vaccinated.
Another type of lymphocyte that is found in low number in healthy animals is the granular lymphocyte, shown in the bottom right panel. Granular lymphocytes are distinguished by the presence of small pink granules collected into one area of the cytoplasm. Not all lymphocytes in blood smears are round. Some are distorted into other shapes by the mechanical forces applied to them during smearing and some are molded by contact with red cells.
eosinophil species differences
Eosinophil granules in most animals are orange but there are always exceptions. The granules in eosinophils of iguanas and some birds are actually pale blue. In general, nuclei of mature eosinophils are shorter and less segmented than neutrophil nuclei and the cytoplasm, if visible, is pale blue. Marked species variation exists regarding the number, size, and shape of eosinophil granules.
The most intraspecies variation is found in dog eosinophils. Marked variation in granule size, number and shape occurs within and between individuals of any breed. A specific and predictable morphologic variant of the eosinophil is seen in greyhounds and other sighthounds (eg, whippets, deerhounds). Eosinophils in these breeds lack visible granules and appear as cells with slightly segmented nuclei, gray cytoplasm, and vacuoles. They are sometimes mistaken for toxic neutrophils or monocytes.
Eosinophils of the cat have small rod-shaped orange granules that fill the cytoplasm, while those of the horse have very large globular orange granules. Ruminant eosinophils have many small very round orange granule
basophil species differences
Prototypical basophils of human blood are filled with small, round, dark purple granules. Similar basophils are found in some species but not in others.
baso Canine basophils are difficult to recognize since many do not have readily apparent granules. The major identifying features of canine basophils are the long and folded nucleus, described as ribbon-like, and the unusual gray to lavender hue of the cytoplasm. Some basophils contain a few purple granules. Basophils are rare in blood of healthy dogs.
Feline basophils are packed with small, slightly oval granules that are pale lavender rather than deep purple. The nucleus in many appears to have vacuoles, which are actually granules lying on top of the chromatin. Basophils are rare in blood of healthy cats.
Basophils of horses and ruminants are similar to each other and to human basophils. These cells contain many small deep purple granules that obscure the nucleus in many cells. Arrows point to nuclear lobes in the picture of a cow basophil. Some basophils have few granules, which probably is the result of degranulation in the sample. Low numbers of basophils are commonly found in blood of healthy cattle and horses.
reactive lymphocytes
Reactive lymphocytes are seen in peripheral blood as a response to antigenic stimulation. Thus, they are more frequently in younger animals, who are antigenically naive. Any disease process can induce antigenic stimulation and result in the presence of reactive lymphocytes in circulation, thus it is a relatively non-specific finding. Reactive lymphocytes are heterogeneous - they vary in size and morphologic features (nuclear shape, amount and color of cytoplasm). They all have relatively mature clumped nuclear chromatin and no visible nucleoli. Their nuclear shapes vary quite markedly. Some have increased amounts of deep blue cytoplasm with perinuclear clear zones (representing the Golgi) and resemble plasma cells. This heterogeneity in size, shape and appearance (see images below) is most compatible with a reactive lymphoid population.
Since some reactive lymphocytes can be quite large and slightly unusual in appearance (see above images E to J), it is of paramount importance to distinguish reactive lymphocytes from neoplastic hematopoietic cells. This is best done by an experienced clinical pathologist, who uses a variety of information (signalment, clinical signs, morphologic features of the cells in question), to make a distinction between reactive lymphocytes and neoplastic cells. However, this is not always possible and when cells that cannot be readily identified are observed in circulation, repeat testing and evaluation of the animal for hematopoietic neoplasia is indicated.
Reactive lymphocytes (all taken at the same magnification) in a older dog with an atrial hemangiosarcoma. A: Normal small, mature lymphocyte. B: Small "plasmacytoid" lymphocyte: this cell has increased amounts of darker blue cytoplasm than normal. C: Another variant of a "plasmacytoid" lymphocyte. The adjacent neutrophil indicates the lymphocyte is small. D: Another variant of a "plasmacytoid" lymphocyte with more abundant cytoplasm and a perinuclear clear zone. E: A large reactive lymphocyte. This cell has cytoplasmic vacuoles, medium blue cytoplasm, but a coarse chromatin with no nucleoli. F: A larger "plasmacytoid" lymphocyte. G: Large reactive lymphocyte with a pleomorphic nucleus and smooth dark blue cytoplasm. H: Large reactive lymphocyte with "bi-lobed" nucleus. I: Large reactive lymphocyte with pleomorphic nucleus, deep blue cytoplasm and cytoplasmic vacuoles. J: Another variant of a large reactive lymphocyte with a pleomorphic nucleus.
blood cell lineage
Normally matured segmented and late band neutrophils, shown in panels A and C, have white cytoplasm with pink granules, long and fairly narrow nuclei and tightly condensed chromatin. Segmented and band neutrophils with toxic change (examples shown in panels B and D) have less condensed chromatin than their normal counterparts and bluer cytoplasm due to retention of ribosomal RNA.
These images are from an iron deficient alpaca that also had an inflammatory leukogram due to an enteritis.
A: The two cells are a segmented neutrophil (upper cell) and a band neutrophil (black arrow). Toxic change is evident in both cells - cytoplasmic vacuolation and toxic granulation in the segmented neutrophil and cytoplasmic basophilia in the band neutrophil.
B: Three segmented neutrophils are shown, all of which are toxic, demonstrating toxic granulation (upper two cells identified with the red arrows) and cytoplasmic vacuolation (all three cells). The red blood cells in the background are hypochromic (have less hemoglobin than normal) which is a cardinal feature of iron deficiency.
hypersegmented neutrophil
