Today we're going to talk about some very special protectors in our bodies. You may or may not have heard of them, but let's just talk about them today. These are the 'natural killer cells' or as we call them , ``NK cells'' . Does the name sound a little scary? But these are actually our best friends, protecting us from getting sick.
What are these natural killer cells (NK cells)?
Simply put, `(NK cells)` are a special type of white blood cell in our body. Like police officers, they sneak into our bodies and seek out and destroy disease-causing infected cells and cancer cells. So you can see that these `(NK cells)` are very important soldiers in our immune system . Our immune system is what protects us from harmful invaders called `(Pathogens)` like viruses, bacteria, parasites, and cancer cells that enter our body.
These `(NK cells)` belong to a special group of white blood cells called `(Lymphocytes)`. You may have also heard of `(B-cells)` and `(T-cells)`, they are also members of this `(Lymphocytes)` family.
Do you know why these cells are called 'natural' killers ? The reason is that they can destroy cells that pose a threat to our body without any training, that is, without prior recognition. Some other types of `(Lymphocytes)`, for example `(Cytotoxic T-cells)`, need to recognize the pathogen in advance in order to destroy a harmful cell. But our `(NK cells)` are not like that, they are naturally good at this job!
What actually happens to natural killer cells (NK cells)?
Okay, now let's see what these `(NK cells)` do exactly. Their main job is to destroy cells that were once healthy but now pose a threat to our bodies. This includes cells that have been infected with viruses, as well as cells that have become cancer cells. What these `(NK cells)` do is to catch and destroy these harmful cells at the earliest stage. Then they stop spreading throughout the body. Imagine this, it's like catching a thief trying to break into a house.
Natural killer cells are the main fighters in our innate immune system . This innate immune system is a very important defense system in our body. Simply put, this is the first line of defense against any threat that comes into our body. This includes physical barriers such as our skin and mucous membranes. These prevent pathogens from entering the body. Also, this innate immune system includes special immune cells such as NK cells. These cells destroy threats that have entered the body by crossing those physical barriers.
Although the main job of an NK cell is to kill other cells, these cells do another important thing. That is to communicate . They release special proteins called cytokines. What these cytokines do is send messages to other cells in our immune system, saying, 'There is a problem here, come and attack these harmful cells.' It's like bringing in more troops to help in a battle.
How do these natural killer cells (NK cells) work within the immune system?
Isn't it amazing how these `(NK cells)` work? Think of them as police officers patrolling our bodies. They examine each cell and ask, 'Is this a healthy cell? Or is this a sick cell that doesn't belong in our body?' When they do this, if they detect a cell that is harmful, they release deadly chemicals into the cell to destroy it.
Now the question is, how does an `(NK cell)` decide whether to kill a cell or not? It is decided based on the signals that the `(NK cell)` receives (or does not receive) from the cell being examined (let's call it the 'target cell').
An NK cell has many special receptors on its surface. These receptors work together to determine whether an NK cell will kill a target cell or inhibit it.
How to stop cell death (Inhibition)
Natural killer cells do not attack cells that have markers that identify them as healthy, self-cells. MHC-1 is the main cell marker that identifies an NK cell as 'self'. This MHC-1 marker on the target cell binds to an inhibitory receptor on the NK cell. This binding causes the NK cell to stop killing. It's like stopping a car at a red light. The NK cell then moves on to the next cell.
Activation of cell killing
Natural killer cells are activated to destroy target cells that they recognize as 'not our own'. These include:
- Cells that release active signals: Cancer cells and infected cells sometimes release special chemical signals. These signals prompt ``NK cells`` to attack them.
- Cells with no or reduced MHC-1 expression: NK cells kill cells that do not express MHC-1. Sometimes, even if a cell has MHC-1, it may be reduced in quantity. That is, less than normal. For example, a viral infection can reduce the expression of MHC-1 in a healthy cell. Think of it like catching someone without an ID card.
`(NK cells)` use chemicals called `Perforin` and `Granzymes` to kill a target cell. `Perforin` creates a hole in the target cell. Then `(NK cells)` can insert `Granzymes` through that hole. Those `Granzymes` are what destroy the cell.
Activated NK cells do something else. They release the cytokines I mentioned earlier. They tell other white blood cells to come and help remove this threat from the body.
Where are these natural killer cells (NK cells) located in our body?
Where do you think these important `(NK cells)` are produced? They first start to develop in a spongy tissue inside some of our bones. That's what we call ``bone marrow`` . That's where most blood cells are produced.
When formed in this way, some of the ``NK cells'' may remain in the bone marrow. Others may travel to other tissues and organs in our lymphatic system to develop further. For example:
- Lymph nodes - You probably know those little lumps that sometimes appear in the neck when you have a fever.
- Spleen
- Tonsils - We also call them tonsils.
- Thymus
Once fully mature, our bodies release ``NK cells'' into the bloodstream. Mature ``NK cells'' are found in lymph nodes and related organs. They can also be found in organs like our liver and lungs. That means they're patrolling pretty much everywhere!
How many natural killer cells (NK cells) are there in our body?
Now you might be thinking, 'Okay, if it's that important, how many NK cells do we have in our bodies?' NK cells make up between 5% and 10% of the total lymphocytes circulating in our blood. But their lifespan is a bit short, only about two weeks. But don't worry, because our bodies are constantly making new ones. It is said that an average adult has more than two billion NK cells in their bodies at any given time! Imagine, there is such a large army inside us to protect us.
What diseases are associated with natural killer cells (NK cells)?
What happens if we don't have enough NK cells in our bodies? We are more susceptible to infections and cancer . Because that first line of defense is weakened. Also, research has found that NK cells play an important role in several other diseases. Here are a few examples:
- Autoimmune diseases: These diseases are caused by our own immune cells attacking our own healthy cells. It is thought that some problems with the way NK cells work may contribute to the development of these autoimmune diseases.
- Asthma: NK cells are involved in the inflammatory response in our body. Depending on various factors, NK cells can increase or decrease this inflammation.
- Inflammatory bowel disease (IBD): NK cells are also involved in our body's inflammatory response to bacterial infections in our intestines.
What are the diseases that affect natural killer cells (NK cells)?
There are two immunodeficiency conditions that are specific to NK cells. Both are caused by genetic mutations that are present at birth. A genetic mutation is a change in our DNA, the blueprint that tells our cells how to function.
1. Classical natural killer cell deficiency (NKD): In this condition, there are very few or no NK cells in the blood. To have Classical NKD, you need to have less than 1% of your circulating lymphocytes.
2. Functional natural killer cell deficiency (NKD): In this, even though NK cells are present, they do not function as efficiently as normal NK cells. It is like having weapons but not knowing how to fight.
Both of these conditions make you more susceptible to various infections. For example:
- `HPV` (Human Papilloma Virus)
- Herpes
- Cytomegalovirus (CMV)
- Epstein-Barr virus (EBV)
- Varicella-zoster virus - This is the virus that causes chickenpox.
What is the difference between natural killer cells (NK cells) and cytotoxic T-cells?
You may remember that we mentioned earlier that both `NK cells` and `Cytotoxic T-cells` are members of the `Lymphocytes` family, which destroy harmful cells. However, these two play slightly different roles in our immune system.
- (NK cells): They can attack any cell if they perceive it as a threat . `(NK cells)` belong to our innate immune system . This is our first line of defense against infected and diseased cells. Natural killer cells respond faster than `T-cells`. They start killing within three days of infection. Like a police raid unit!
- (Cytotoxic T-cells): These can only attack cells that contain pathogens that our body has previously recognized . That is, the body must have had the disease before and have a memory of it. These people belong to our adaptive immune system . This system recognizes specific threats and launches targeted attacks against them. It takes about a week after an infection for our body to recognize this specific threat and produce the special `T-cells` needed to fight it. This takes a while, like specially trained commandos.
Simply put, ``NK cells'' are fast-acting defenders who face general threats. ``Cytotoxic T-cells'' are specialists who remember specific threats and only fight them if they come back.
What factors influence the activation of natural killer cells (NK cells)?
We've talked about this a little bit before. Natural killer cells work on signaling pathways involving their activating and inhibitory receptors. They become activated when the signals that stop them from attacking a target cell (for example, those `MHC-1` molecules) are lost, or when their number decreases . That is, when the `(NK cell)` realizes, 'This is not one of us, there is a problem.' They get to work.
Do we all have natural killer cells (NK cells) in our bodies?
Yes, absolutely! Natural killer cells are an essential part of a healthy immune system . Unless you have a genetic condition like the previously mentioned `Classical NKD`, where your bone marrow is unable to make `(NK cells)`, you have `(NK cells)` in your body.
NK cells respond quickly to threats and protect us from infections and diseases. They destroy harmful cells at their earliest stages, preventing the spread of infected cells and cancer cells. So, having a healthy population of NK cells in the body is very important for a healthy immune system.
The most important things you need to remember (Take-Home Message)
Okay, so here are the most important things to keep in mind about the `(Natural Killer Cells)` or `(NK cells)` we talked about:
- (NK cells) are a very important, special type of white blood cell in our immune system. They are like guards in our body, seeking out and destroying disease-causing cells.
- Their main targets are virus-infected cells and cancer cells. They help to destroy these at an early stage and stop the spread of the disease.
- (NK cells) are part of our 'innate immunity'. That means they can recognize threats and act without prior training.
- Whether a cell has the `MHC-1` marker or not determines whether an `(NK cell)` will attack or not. If `MHC-1` is present, it is labeled as `our cell.' Otherwise, it is attacked.
- They are formed in the bone marrow and are also present in the lymphatic system, blood, and organs such as the liver and lungs.
- A decrease in the number of NK cells can increase the risk of infection and cancer. Their function is also affected by some autoimmune diseases and conditions such as asthma.
- `Classical NKD` and `Functional NKD` are rare genetic diseases that affect `(NK cells)`.
Most importantly, having a healthy amount of NK cells in the body is essential for our overall health and protection from disease. So, it's good to be aware of these silent guards inside our bodies, right?
` Natural killer cells, NK cells, immune system, white blood cells, cancer, viral infections, innate immunity, cellular defense
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