Hello, students! 😊
Today, we are learning about Natural Killer Cells (NKCs). These are a special type of White Blood Cells (WBCs), which help protect our body by fighting harmful cells, like virus-infected cells and even cancer cells.
If you are preparing for competitive exams, this is an important topic to know. We will explain it in a simple, easy-to-understand format to help you learn better. This topic is part of General Science in the subject of Biology and is often asked in exams.
Let’s explore NKCs and how they help keep our bodies healthy! 🌟
What are natural killer cells (NK cells)?
Natural Killer Cells, or NK cells, are a special type of white blood cell that protect your body by destroying harmful cells, such as infected cells and cancer cells. They play a key role in your immune system, which is your body’s defense against harmful invaders like viruses, bacteria, and parasites.
◾ Also Read: Composition of Blood Cell
Why Are They Called “Natural” Killers?
NK cells are known as “natural” killers because they can destroy dangerous cells without needing prior exposure to a specific infection or pathogen. This makes them different from other immune cells, like cytotoxic T-cells, which need to recognize a harmful invader before they can act.
How Do NK Cells Help?
NK cells detect and attack:
- Cells infected by viruses.
- Cancer cells that could harm the body.
By doing this, they help keep you healthy and safe from diseases caused by infections and abnormal cell growth.
Key Fact:
NK cells are one of your immune system’s strongest defenders, working quickly to protect you from threats.
What do natural killer cells do?
NK cells are a type of white blood cell that protects our body by destroying harmful cells. They target:
- Virus-infected cells that can cause illness.
- Cancer cells that were once healthy but have turned dangerous.
These cells act quickly to stop the threat in its early stages, preventing it from spreading further.
Part of Innate Immune System
NK cells belong to your innate immune system, which is your body’s first line of defense against harmful invaders. This system includes:
- Physical barriers, like your skin and mucous membranes, which block germs from entering.
- Special immune cells, like NK cells, that fight threats that get past these barriers.
More Than Just Fighters
While NK cells are best known for destroying harmful cells, they also help your immune system by communicating. They release special proteins called cytokines that signal other immune cells to join the fight against infections and harmful pathogens.
Key Fact:
NK cells not only attack threats but also act as team leaders, coordinating your immune system’s defense!
How Natural Killer (NK) Cells Patrol and Protect Your Body
NK Cells: The Body’s Patrol Guards
NK cells move through your body, scanning cells to check if they are healthy or harmful. They use special markers on cell surfaces to decide if a cell should be destroyed. If a cell is harmful, NK cells release deadly chemicals to kill it.
How Do NK Cells Decide?
The decision to attack or leave a cell alone depends on signals received by the NK cell:
1. Inhibition: Recognizing Healthy Cells
- Healthy cells have markers, like MHC-1, that signal to NK cells, “I belong here.”
- The MHC-1 marker binds to the NK cell’s inhibitory receptor, which stops the NK cell from attacking.
- Once this signal is recognized, the NK cell moves on to check the next cell.
2. Activation: Targeting Harmful Cells
NK cells attack cells that either lack proper markers or send danger signals:
- Cells sending activating signals: Cancer or infected cells release chemicals that alert NK cells to attack.
- Cells without MHC-1 markers or downgraded MHC-1: Some harmful cells (e.g., virus-infected cells) reduce or lose MHC-1 markers, triggering NK cells to destroy them.
How Do NK Cells Destroy Harmful Cells?
- NK cells release perforin, which creates small holes in the harmful cell.
- They then release granzymes through these holes, which destroy the cell from the inside.
Teamwork in Defense
When activated, NK cells also release cytokines, which signal other immune cells to join the fight and help eliminate threats.
Key Fact:
NK cells are like skilled detectives, carefully deciding when to act and ensuring your body stays safe from infections and diseases!
Where are natural killer cells located?
Where Do NK Cells Develop and Mature?
Natural Killer (NK) cells begin their development in bone marrow, which is the soft, spongy tissue found inside certain bones.
How NK Cells Develop
- Start in Bone Marrow: NK cells are formed and begin their development in the bone marrow.
- Move to Other Organs: As they grow, some NK cells stay in the bone marrow, while others travel to parts of the lymphatic system, including:
- Lymph Nodes
- Spleen
- Tonsils
- Thymus
Maturation and Release
Once NK cells fully mature, your body releases them into the bloodstream, where they are ready to patrol for harmful invaders.
Where Are Mature NK Cells Found?
In addition to circulating in the blood, mature NK cells are found in:
- Lymphatic tissues
- Organs such as the liver and lungs
Key Fact:
NK cells are strategically located in different parts of the body, allowing them to respond quickly to infections or other threats.
How Many NK Cells Are in Your Body?
- Percentage of NK Cells: NK cells make up about 5% to 10% of the lymphocytes circulating in your blood.
- Short Lifespan: These cells have a lifespan of around two weeks, after which they are replaced by new NK cells.
- Total Count: On average, adults have more than 2 billion NK cells in their body at any given moment.
Key Fact:
Despite their short lifespan, the large number of NK cells ensures your immune system is always prepared to fight harmful invaders.
What are the conditions and disorders associated with natural killer cells?
Why Are NK Cells Important for Your Health?
Having enough Natural Killer (NK) cells is essential to protect your body from infections and cancer. When the number or function of NK cells is low, your immune system becomes weaker, leaving you more vulnerable to diseases.
Role of NK Cells in Other Conditions
Autoimmune Diseases:
- NK cells may contribute to autoimmune diseases if they don’t function properly.
- In autoimmune conditions, immune cells mistakenly attack healthy cells instead of just diseased or infected ones.
Asthma:
- NK cells are involved in your body’s inflammatory response related to asthma.
- Depending on the situation, NK cells can either increase or reduce inflammation.
Inflammatory Bowel Disease (IBD):
- NK cells play a role in managing inflammation caused by bacterial infections in your digestive system.
- Imbalanced activity of NK cells in the gut may influence IBD symptoms.
Key Fact:
NK cells are vital for immunity, but imbalances in their activity may also contribute to certain inflammatory or autoimmune conditions.
Conditions and Disorders That Affect Natural Killer (NK) Cells
NK cells can be impacted by specific conditions caused by genetic mutations. These mutations, present at birth, change the way NK cells develop or function, leading to immunodeficiency disorders.
1. Classical Natural Killer Cell Deficiency (NKD)
- This condition results in very few or no NK cells in your bloodstream.
- To diagnose classical NKD, less than 1% of your circulating lymphocytes must be NK cells.
2. Functional Natural Killer Cell Deficiency (NKD):
- In this condition, the NK cells are present but do not work as effectively as normal NK cells.
Impact of NK Cell Deficiencies
Both types of NKD weaken your immune system and make you more prone to infections caused by:
- HPV (Human Papillomavirus).
- Herpes Virus.
- Cytomegalovirus (CMV).
- Epstein-Barr Virus (EBV).
- Varicella-Zoster Virus (which causes chickenpox).
Key Fact: These conditions highlight the critical role of NK cells in defending the body against infections, especially viral ones.
Frequently Asked Questions (FAQs)
What is the difference between natural killer cells and cytotoxic T-cells?
Both Natural Killer (NK) Cells and Cytotoxic T-Cells are types of white blood cells that help protect your body by destroying harmful cells. However, they work in different ways and have distinct roles in your immune system.
What NK Cells Do:
- NK cells are part of your innate immune system, which is your body’s first line of defense against infections and diseases.
- They can attack any cell they see as a threat, such as infected cells or cancer cells.
- NK cells work quickly—starting to destroy harmful cells within 3 days of infection.
What Cytotoxic T-Cells Do:
- Cytotoxic T-cells are part of your adaptive immune system, which is responsible for recognizing specific threats your body has encountered before.
- These cells only attack infected cells that contain pathogens (like viruses) that your body has already met.
- It takes about a week for your immune system to recognize a new threat, create the right T-cells, and start fighting it.
Key Difference:
- NK cells respond fast and attack any harmful cell.
- Cytotoxic T-cells are slower, but they target specific pathogens your body has encountered before.
What triggers natural killer cells?
Natural killer (NK) cells function by using a complex signaling process through their activating and inhibitory receptors. These receptors help NK cells decide whether to attack or not.
- Inhibitory receptors: When NK cells detect certain signals, like MHC class I molecules, on a target cell, they do not attack. These molecules act as a “do not attack” signal, telling the NK cell that the cell is healthy.
- Activating receptors: If the target cell is missing these signals or has reduced levels of MHC class I molecules, the NK cell becomes activated. This triggers the NK cell to attack and destroy the harmful cell.
In simple terms, NK cells are like security guards that check for signals on each cell. If they see a warning sign (healthy cell), they move on. If the warning sign is missing or weak (indicating a threat), they attack the cell to protect the body.
Do we all have natural killer cells?
Natural killer (NK) cells are a crucial part of a healthy immune system. They help protect your body by identifying and attacking harmful cells, such as those infected by viruses or cancerous cells.
Unless you have a genetic condition called classical NK cell deficiency (NKD), which affects the production of NK cells in the bone marrow, your body naturally has NK cells. This condition makes it difficult for the body to produce NK cells, leaving you more vulnerable to infections.
Major Source of this Article: my.clevelandclinic.org
