Lymphocytes are cells that mostly reside in the lymph nodes. A lymphocyte is a type of leukocyte.
They are activated by signs of infection in the body, at which point, they grow larger and divide before traveling to the site of the infection. Their job is to kill the pathogen that is causing the infection of the tissue.
There are several types of lymphocytes, and you can tell them apart under a microscope by looking at the receptors on the surfaces of the cells and observing their behavior, including how they impact immunity.
Lymphocytes can be classified into 3 different cell types: B cells (also known as B lymphocytes), T cells (otherwise called T lymphocytes), and natural killer cells.
Now, in your average person without existing health conditions, between 25% and 30% of all leukocytes in their body will be lymphocytes.
That might sound like a fairly low percentage, but this actually means that up to 2 trillion of a healthy person’s cells are lymphocytes!
Lymphocytes are essential for immune function. Not only can they react and combat pathogens in the body quickly, but T lymphocytes and B lymphocytes are also able to memorize antigens once they encounter them.
When T cells and B cells remember antigens to which they have been exposed, they can destroy the same antigen much more quickly in the future. That’s why you might hear T cells and B cells referred to as memory cells.
If you want to truly understand lymphocytes, the best way is to observe them under a microscope. Here’s how to do it:
Microscopy For Lymphocytes
Lymphocytes can be observed in a blood smear on a microscopic level. This is done using a stain called Wright’s stain, and this staining method is used for bone marrow samples in addition to blood smears.
You Will Need
- Fresh or EDTA-stored blood sample
- 2-3 glass slides
- Compound microscope
- Cover slip
- Beaker
- Pipettes
- Drying rack
- Wright’s stain
The Process
When you have all the equipment required to perform the stain, you will start by putting a single drop of the blood sample onto one of the glass slides.
Make sure that the slide is clean so that it doesn’t contaminate your sample!
Next, you’ll take another one of your glass slides (or you can use the cover slip if you hold it at the right angle) and spread out the drop so that it forms an even, thin film across the original slide.
At this point, you will want your drying rack to be ready and easily accessible because you need to be able to place the slide straight on the rack so it can air-dry.
When the slide is dry, you’ll take your Wright’s stain solution and a pipette. Using the pipette, extract 1 ml of the stain solution and carefully add it on top of the sample slide.
Wait 3 minutes before adding a couple of drops of phosphate buffer at a 6.8 pH, or you can use distilled water instead. Wait 5 more minutes.
Rinse off the slide, and after waiting for it to dry, remove any remaining stain from the back of the slide. Then, set your microscope to low power and observe the slide under the microscope.
When you set your microscope to 1000x, you’ll need to use immersion oil.
Any lymphocytes you see under the microscope will be dark purple in color. You can see the nucleus of each cell because it should be dark blue, while the cytoplasm will be more of a sky blue color.
Discussing Types Of Lymphocytes
Lymphocyte cells are types of agranulocytes. Agranulocytes are cells without granules. Cellular granules are particles found in the cytoplasm. Under a microscope, granules look like tiny dots.
You won’t see these when you observe a lymphocyte microscopically, unless the lymphocyte is especially large, in which case you might see a few granules.
It should be easy to identify lymphocytes in a blood smear because they should account for anywhere between 20% and 30% of the leukocytes in the sample.
Lymphocytes’ main function is to find antigens in the body and destroy them. They do this by building two kinds of immune responses: cell-mediated immunity and humoral immunity.
Humoral immunity is mostly concerned with the lymphocytes’ ability to identify the cells that need to be removed, whereas cell mediated immunity involves actually destroying cancer cells and infected cells.
When an antigen appears in the body, it activates the B cells. This triggers the body to create antibodies that match the antigen. Therefore, B cells are crucial for humoral immunity.
The antibodies don’t stop circulating through the body after this, which means that they can recognize antigens of the same type if they appear again.
Meanwhile, T cells are responsible for cell mediated immunity. These cells travel to the infection site and actively kill the particles responsible for the infection.
Now, T cells can be one of several types. These include:
T Helper Cells
T helper cells, also called helper T cells, helper T lymphocytes, or CD4+ cells are really important for the human body’s immune response.
These cells release a protein called CD4 from the surface of the cell.
This protein is what allows the helper T cells to activate because it binds class 2 MHC molecules, and these are key in the recognition of dangerous substances and cells in the body.
Cytotoxic T Cells
Cytotoxic T cells are the lymphocyte cells that actually destroy the infected or cancerous cells.
The way cytotoxic T cells work is fascinating. They program cancerous or infected cells to undergo a process called apoptosis (cell death).
The programming can take place in as little as 5 minutes, and the cells will die within hours. As you can see, cytotoxic T cells are extremely effective components in the immune system.
Cytotoxic T cells are able to find the cells that they need to destroy by locating antigens that are bound to the MHC protein mentioned earlier, demonstrating how different types of lymphocytes work together to combat infection in the body.
Regulatory T Cells
These cells are also called suppressor cells because their role is to suppress some of the responses produced by other T cells as well as B cells.
In doing so, Regulatory T cells prevent the onset of autoimmune conditions as well as chronic inflammation while building your body’s peripheral tolerance.
If other T cells and B lymphocytes are left to their own devices, the body’s immune response may become overactive.
When this happens, the immune system begins to attack cells that are not infected or cancerous, leading to autoimmune conditions.
To prevent this, suppressor cells secrete tolerogenic cytokines, which activate other cells known as effector immune cells. These cells protect the body while other lymphocytes target the infection.
Final Thoughts
Lymphocytes are incredibly important for maintaining a healthy immune system. They can be observed under a microscope from a blood sample using Wright’s stain and a compound microscope.
These cells can be identified by their lack of granules, dark blue nucleus, and sky blue cytoplasm.
The different types of lymphocytes are T cells, B cells, and natural killer cells. T cells can be divided into three more categories: regulatory T cells, Cytotoxic T cells, and T helper cells.
All of these cells play crucial roles in the human body’s immune function.
T helper cells identify the infected cells, Cytotoxic T cells target those cells, and natural killer cells protect the body from the effects of an overactive immune response.
Making up between 20% and 30% of the leukocytes in the human body, lymphocytes are some of the most fundamental cells for health and wellbeing.
Ever since I was a little girl, I have been fascinated by science. Every holiday I would ask for the newest science kit, and spend weeks learning with it.
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