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Unlock This CourseYour body is constantly under attack from harmful microorganisms like bacteria, viruses and fungi. Fortunately, you have an amazing defence system called the immune system. White blood cells are the soldiers of this system, patrolling your body and fighting off invaders to keep you healthy.
Key Definitions:
Unlike red blood cells, white blood cells have a nucleus and can change shape. They make up only about 1% of your blood, but they're incredibly powerful. Most importantly, they can leave your blood vessels and move through tissues to hunt down pathogens wherever they hide.
There are several different types of white blood cells, each with their own special job in protecting your body. Think of them as different specialists in your body's army.
Each type of white blood cell has evolved to tackle threats in different ways. Some engulf and destroy pathogens directly, whilst others produce chemical weapons to neutralise invaders.
These are the 'eaters' of the immune system. They engulf and digest pathogens, dead cells and debris. Neutrophils and macrophages are the main types of phagocytes.
These include B-cells and T-cells. B-cells produce antibodies, whilst T-cells can directly kill infected cells or help coordinate the immune response.
Eosinophils fight parasites and are involved in allergic reactions. Basophils release chemicals that cause inflammation and help recruit other immune cells.
Phagocytes are like the body's cleanup crew and first responders. When they detect a pathogen, they spring into action with a process called phagocytosis.
Step 1: The phagocyte detects and moves towards the pathogen using chemical signals.
Step 2: It surrounds the pathogen with its cell membrane, forming a bubble called a phagosome.
Step 3: Digestive enzymes break down the pathogen inside the phagosome.
Step 4: The harmless remains are expelled from the cell.
Neutrophils are the first responders - they arrive quickly at infection sites but die after a few days. Macrophages are the heavy artillery - they're larger, live longer and can engulf bigger targets. They also help clean up the battlefield after an infection.
Whilst phagocytes provide general protection, lymphocytes offer targeted, specific immunity. They can remember previous infections and respond faster and stronger if the same pathogen returns.
B-cells are like specialised weapons manufacturers. When they encounter their specific antigen, they transform into plasma cells that pump out thousands of antibodies per second. These antibodies are Y-shaped proteins that bind to antigens like a lock and key.
Antibodies are incredibly specific - each one can only bind to one particular antigen. Once attached, they can neutralise pathogens in several ways:
When you catch influenza, your B-cells produce antibodies specific to that flu strain. These antibodies bind to the virus particles, preventing them from infecting your cells. Memory B-cells remember this encounter, so if you meet the same flu strain again, you'll be protected. However, flu viruses mutate frequently, which is why you can catch flu multiple times and need yearly vaccines.
There are two main ways your body can become immune to diseases: actively making its own antibodies, or receiving ready-made antibodies from elsewhere.
This occurs when your own immune system produces antibodies in response to an antigen. It takes time to develop but provides long-lasting protection because memory cells are formed.
You get this by catching and recovering from a disease. Your immune system learns to recognise the pathogen and remembers it for future encounters. Examples include chickenpox or measles immunity after infection.
This comes from vaccination. Vaccines contain weakened, dead, or parts of pathogens that trigger an immune response without causing serious disease. Your body produces antibodies and memory cells just as if you'd had the real infection.
This involves receiving ready-made antibodies from another source. It provides immediate protection but doesn't last long because no memory cells are formed.
Babies receive antibodies from their mothers through the placenta during pregnancy and through breast milk after birth. This protects newborns during their first few months when their immune systems are still developing.
This involves injecting antibodies from another person or animal. It's used for immediate protection against serious diseases like rabies or snake bites, where there's no time to wait for active immunity to develop.
Vaccines are one of medicine's greatest success stories. They've eliminated smallpox worldwide and dramatically reduced diseases like polio, measles and whooping cough.
1. Introduction: The vaccine introduces antigens (from weakened, dead, or parts of pathogens) into your body.
2. Recognition: Your immune system recognises these antigens as foreign.
3. Response: B-cells produce antibodies specific to the antigens.
4. Memory: Memory B-cells and T-cells are formed and remain in your body.
5. Protection: If you encounter the real pathogen later, memory cells quickly produce antibodies to fight it off.
Different vaccines work in slightly different ways, but all aim to train your immune system to recognise and fight specific pathogens.
When enough people in a community are vaccinated, it creates 'herd immunity' that protects everyone, including those who can't be vaccinated due to medical conditions.
If most people are immune to a disease, the pathogen can't spread easily through the population. This protects vulnerable individuals like newborn babies, elderly people and those with weakened immune systems who rely on the community's protection.
In recent years, some communities have seen measles outbreaks due to declining vaccination rates. Measles is highly contagious - one infected person can infect 12-18 others. When vaccination rates drop below about 95%, herd immunity breaks down and outbreaks can occur, putting unvaccinated children and vulnerable adults at risk.