Learning Page

This page is intended for students and researchers that are just getting started with leukocyte-related projects. Here, there is information on microscopic identification of leukocytes of model animals, starting with amphibians. Note, that learning to identify leukocytes takes some skill, which needs to be honed after a considerable learning period.

For instructions on making blood smears, see this website

 

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Amphibian Leukocytes

The cells pictured below are from bullfrog tadpoles (Rana catesbeiana), and are generally typical of amphibians. (An atlas of amphibian cells can be downloaded in the further reading page)

The lymphocyte is the most common white blood cell in amphibian blood smears. With giemsa staining, it typically appears as a small, blue , circular cell, occasionally with cytoplasmic projections. The majority of the cell is filled by the round , blue nucleus, and there is only a faint ring of light-blue cytoplasm around it.

There are large, medium and small lymphocytes, and some authors choose to count each separately, others lump them together. Large lymphocytes can be confused with monocytes, though monocytes typically have a smaller nucleus and more greyish cytoplasm.

Neutrophils are the second-most common leukocytes in amphibian blood smears. They are generally rounded and have a faint-pink color. The nucleus is lobed, as in the picture to the left (note the constricted part that divides the two lobes). These lobes can give an indication as to the age of the cell - young neutrophils only have one lobe, older cells have two or three. Because of this, some authors report the number of young cells (also called 'band' cells) separately from the number of 'segmented' cells.

These cells may be the easiest leukocytes to identify, due to their red-staining granules in the cytoplasm. Like neutrophils, the nucleus is lobed, although it tends to be obscured by the granules.

Between 1-15 percent of all leukocytes are eosinophils in most amphibians, except for the Ambystomatid salamanders, which appear to have between 20-50% (Davis and Durso In Press). Also, eosinophil numbers increase during metamorphosis in amphibians, then return to low levels post-metamorphosis (see Davis 2009).

These cells are nearly always purple (with giemsa staining), making them easy to spot. The purple is from the granules, which are abundant in the cytoplasm, and tend to obscure the nucleus. These cells are generally small and not always round. In most amphibians, less than 10 percent of leukocytes are basophils.

Monocytes can be tricky to identify, because of their similarity to large lymphocytes. Also because they tend to be scarce in blood smears. Typically, there are less than 5% monocytes in amphibian blood smears.

Monocytes are usually large, with a variety of shapes (i.e. not always round), and have a faint-blue color. The nucleus is bluish, and not lobed. The best way to identify monocytes is their nucleus to cytoplasm ratio - in monocytes, the nucleus only takes up half or two-thirds of the cell. In lymphocytes, it is more like 90%. There also tends to be some vacuoles in the cytoplasm, such as in the cell to the left.

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Avian Leukocytes

The cells pictured below are from Charlie the cockatiel, and are generally typical of birds
These cells are small, round and light-blue with giemsa staining. They are the most abundant white cell in passerines but other avian groups have more heterophils than lymphocytes. As with amphibians, the nucleus of avian lymphocyte s takes up most of the cell, leaving only a faint, light blue ring of cytoplasm around it. These can be small or large, and large cells can be confused with monocytes.

Avian heterophils are the equivalent to mammalian and amphibian neutrophils functionally, though they look different. Like neutrophils, they have a lobed nucleus, but in contrast, there are many rod-shaped, red- or pink-staining granules in the cytoplsm. These granules are comparable to those of eosinophils, which have orange-staining, round granules.

In passerines, heterophils make up between 7-20% of the leukocytes, though some species appear to have extremely few (5% or less), such as House Finches and Dark-eyed Juncos.

Avian eosinophils are much like those of other taxa, being generally round, having a lobed nucleus and with many orange, round, cytoplasmic granules. In some species, these may not stain very well (like the cell pictured), and it can be difficult to view them.

Most birds generally have 5% or fewer eosinophils in circulation.

Basophils in birds look like those of other taxa. They are easy to spot thanks to their purple-staining grnaules, which tend to obsure their nucleus. There's not much else on a smear that stains this color. There tend not to be many of these cells in most birds.
Avian monocytes are large cells (relative to erythrocytes) that are esily confused with large lymphocytes. Their nucleus is light blue, though it often has a lattice-like appearance throughout. The big difference between lymphocytes and monocytes is in the amount of space taken up by the nucleus. In monocytes, it is between half to three-quarters of the cell. In lymphocytes it is more like 90% of the cell.