#leukogram

We talked about blood smears before and they are showing up again! Leukograms are the portion of the CBC pertaining to white blood cells. White blood cells are the surveillance team for the body, killing pesky bacteria, cleaning up after themselves, directing healing, and so much more. They are fantastic little cells!

An analyzer is a great thing to have in a veterinary practice and there are varying kinds, each with their pros and cons. The downside of all of them is that they cannot do your job for you! That means making a blood smear, drying it, staining it, and then sitting your butt down at the microscope to evaluate it. Your blood count just is NOT complete without a blood smear.

We’ll talk about neutrophils, monocytes, lymphocytes, eosinophils.  Basophihls I will not really talk about because they are rarely seen and we know so little about them that it’s not useful for me to speculate on them here.

Let’s look at some White Blood Cells (WBCs)

Cells we expect to see besides Red Blood Cells and Platelets,

Neutrophils

These guys are the first responders and they phagocytize (internalize and kill) bacteria. Fun fact, they are the main component in pus of most of our domestic species. Some animals, like rabbits, do not have neutrophils, but a slightly different cell to serve a similar function!

They look different in different species, but serve the same basic function.

The band neutrophil shown at the bottom is an immature form, whereas the others are called ‘segmented’. The presence of band neutrophils in itself is not a problem. Animals make more of them all the time. When the storage of mature cells has been depleted, we expect to see an increased number of band neutrophils. The body will pump out immature neutrophils instead of having none to put out at all. What’s the issue?

Band neutrophils are not as competent as their mature counterparts are. When band neutrophil numbers get high while segmented neutrophils are low, this is termed a ‘left shift’. If we have an infection, we want increased numbers of both segmented and bands!

What happens when we hurry?

Neutrophils undergo ‘toxic’ changes. These are not due to the presence of toxins, but indicate the hurried way the bone marrow is producing and pumping out the immature neutrophils. This includes a ‘foamy’ appearance of the cytoplasm, cytoplasmic basophilia (looks more purple) meaning that RNA has been retained, and the presence of Dohle bodies which are aggregates of RNA.

If you missed the last part about neutrophils, find it here!

Today we are going to talk about monocytes (macrophages when they get into tissues). Some of them have a name based on where they are end up in the body, which I think is silly. Alas, I have no naming or renaming rights. Neutrophils like to show up within the first 24 hours of infection as the first responders to insult. Consider the monocytes as the back-up that gets called in.

The professional phagocyte who are better at killing than neutrophils, the cells that clean up debris, and the cells that guide wound healing. (I freaking love these cells!)

Their appearance is quite variable even within a species. As my professor remarked, when she retires, she plans on collecting the whole alphabet of them to put up on her walls. Clinical pathologists, ya know? 

 If you remember the last time when we talked about neutrophils, you may notice that some of these are difficult to differentiate from a band neutrophil. The monocyte is typically larger than a band neutrophil and will have a nucleus with ‘smoother’ edges and a slightly more basophilic (blue/purple) cytoplasm. This takes time to get practiced at differentiating them. When in doubt, I try to compare the size and look for the change in cytoplasm color.

Monocytes are also special because they differentiate and proliferate out in the tissues. They can become a resident macrophage of a tissue they end up in or a dendritic cell. Once they are out in the tissue, they phagocytize foreign material, bacteria. After breaking these down, they present little pieces (antigens) to lymphocytes as a way of recognizing this invader. Beyond this, macrophages are critical in the healing process. They break down damaged collagen, cells, and direct the process of healing. They also secrete a variety of cytokines (chemical signals).

In the context of our leukogram, increased number of monocytes indicates an infection somewhere in the body.