Published on October 22, 2014
How do lymphocytes function, and what's age have to do with it? When it comes to understanding your lab tests, laboratory scientist Dr. Susan Leclair extends her discussion on lymphocytes and their morphology to help patients make sense of it all.
Transcript | Be Smart About Your Lab Tests: Understanding Lymphocyte Morphology
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Okay. Welcome to Patient Power, actually number two on lymphocytes. There will be several of these, so this is just to keep you and me on track. The last time we talked about the immunological function of lymphocytes. This time we're going to talk about how they look inside the blood and what do we know from their morphology.
So we're really going to talk about some funny names. And, again, as I said in the very first one of these about granulocytes, hematology is a young science. It really didn't get started until the early part of the 20th century, and a lot of that was wrong, as we have learned. So there's the old nomenclature that, you know, the great guru had, and no one wants to fix that. And then there's the correct nomenclature, and then there's the one the North uses and the West uses, so there's a lot of words that we're going to be talking about today in this.
Here's our problem. T lymphocytes and B lymphocytes, you remember them from the last time, they look alike, mostly. The little, small differences between them we're not going to talk about. So, no, I cannot tell looking at a microscope whether the lymphocytes I'm seeing are T cells or B cells.
So what am I looking for then? Isn't that the most important thing? I can look at their age, and I can see whether they're functioning. The earliest recognizable cell of any series has the suffix blast attached to it. So if I was looking at the earliest recognizable lymph, it would be a lymphoblast. If I was looking at the earliest recognizable red cell, it would be normoblast. That's a long story. We'll get to that later.
So as shorthand for most people is if somebody says that there are blasts there, they really mean the earliest recognizable cell of a series. And since they all tend to look alike, most places will not say lymphoblast or normoblast or some other blast. They'll just say blast, additional testing to absolutely confirm which cell line it is must follow. So a blast right now is a blast is a blast.
So the earliest recognizable lympho—is a lymphoblast. T or B makes no difference. They don't really have much in the way of function. The big thing about a lymphoblast is that it can grow. It can multiply. It can undergo mitotic division over and over and over again so that if you have one that's a little bit uncontrolled, it will continue to reproduce and reproduce and reproduce, and you build a clone of that one cell.
You don't want a single clone of lymphoblast. You want clones that are going to be T cells, clones that are B cells, clones that are NK cells, clones that are other subsets we're not going to talk about cells. So it's not nice to know that we can't tell them apart without having really specialized testing for it.
So we have lymphoblasts, and then we have lymphocytes, T or B, doesn't make any difference, usually kind of small. They can range from again the size of a red cell maybe to the size of two red cells stuck together, so they're not particularly big. They're not like granulocytes. They don't go hunting for anything. They're rather passive cells. If you want them to do anything, you bring the antigen to them, and then they will take care of it. But they're not going to go hunting for any trouble.
They're just going to passively circulate, and they circulate in two different places. They circulate in the blood cells, in the bloodstream, and they circulate in the lymphatics, that's a circulation that's parallel to the blood circulation. The only thing that goes in there are lymphocytes and lymph fluids. So you can see these two circulations as having connections to them, but they're kind of like one-way connections for the other cells that can't get in. Only the lymphs can get into the lymphatic fluid. Care.
Why do I care? Because that's how lymphocytes communicate with each other. If I have one lymphocyte, and it suddenly has been told by a T lymphocyte to turn on and make antibodies, well, it's going to have to recruit other cells to do it as well, so it's going to get into those lymphatic fluids, find its friends, and they will get together and form a clone of cells that are going to create that antibody that you want.
So there's a lot of activity that's going on in these cells, and that makes their morphology different. The lymphoblasts are look—they're young. They don't have any function. They're somewhat featureless in their cytoplasm. They just kind of lay there and do almost nothing.
Mature lymphocytes are rather neat, prim almost. They are relatively well organized. They know exactly what it is that they're going to do. And like specialists, they know that they're only going to do one thing or maybe two at most, so they have a very orderly, organized way to them in the way that they look and in the way that they stain.
But then there's one in between. I take this mature, prim, proper, you know, like the lady that sits with her legs crossed and her arms folded in front of her, and I say to that person, I want you to do 17 things, and I want you to do them in a hurry. Well, she's not going to be prim anymore. She's going to be a little bit looser. She may be a little bit bigger. She may move her arms around. There may be some changes in her morphology.
Well, that's what happens here. These memory cells all of a sudden say, oh, well, I have to make a huge monoclonal number of these cells in order to fight off my strep throat, so they're going to have to get busy. So the first thing that happens to these cells is they're going to get larger. They are going to have a much bigger cytoplasm because now they're going to have to make protein, and proteins are made in the cytoplasm, so I need more cytoplasm.
I need a more active nucleus, because the nucleus is going to be busy telling the cytoplasm what to make. So now I have a bigger cell. I have a cell with what's called fulminant cytoplasm or abundant cytoplasm like the pictures that you're seeing. They're bigger. They're more flamboyant looking.
Originally, in the 1920s, a physician looked at them and thought, oh, my god, they're damaged, they're evil, they're atypical, which is a medical term meaning diseased. By the time Bob Good got around to looking at these cells in his new vision of the immune system, he said, these cells aren't diseased, they're not damaged, they're not in trouble. They're defending us, so we shouldn't call them atypical because atypical means bad. We should call them reactive or stimulated.
So now you'll see on different differentials on your reports some places still use the word "atypical," because they haven't changed it, and some have moved on to reactive. What is a reactive lymphocyte? It's a lymphocyte doing its job. It doesn't mean that it's diseased. It means you have a cold. It means you have an immunization response. It means that you have strep throat.
It means that you have a functional immune system, which is the important part of it. The more of them you have, the more antigenically stimulated they are, the more noticeable they are. The classic disease in which you find reactive lymphs is infectious mononucleosis, and there you might have 70 percent of your cell being reactive lymphocytes. Most of the time you have a cold, you have strep throat, you have immunizations, maybe 10 to 20, maximum 30 percent of your cells will be reactive.
To think about it, you've got three different kinds of morphologies here: young, immature, doesn't really know what it's doing but is willing to grow up if you want it to. You've got a small, round, resting a lot of times is what we call it, lymphocyte that knows exactly what it's supposed to do and will do it when you need it but won't do it when you don't need it.
And then you've got these kind the transitional cells called reactive that are there to fight off whatever is causing your immune response at that time. So it's February, it's been raining, snowing, sleeting for six days. And you go to have your blood test done, and the CBC result comes back few reactive lymphocytes. I want them to be there, because you cannot tell me after six days of going to see your friends and going grocery shopping and going out that you have never come in contact with any antigen in those six days.
I want to see them. They're a good thing for me. I don't want to see them at 60 percent. I don't want to see them at really, really high numbers, but I want to see them, because that means that your immune system is functioning. And if I don't see them, that either means you haven't really come up against strep throat lately, or your immune system is not functioning correctly.
So when you look at the word "reactive," don't worry about it as much. The word to be concerned about if you ever see it is the word "blast," because that means something is seriously wrong.
Again, lymphocytes are complex. There's a lot of questions I know. Don't forget to send them to email@example.com. And remember that knowledge is one of your best medical treatments.
And next time we'll talk about lymphocytes in terms of that transition between lymphoid organs like the spleen and the thymus and the bone marrow and the peripheral blood. Good day.