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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: White Blood Cells and Immunity
Your body is constantly under attack from microorganisms that could make you ill. Luckily, you have an amazing defence system called the immune system. White blood cells are the key players in this system, working tirelessly to protect you from harmful invaders.
Key Definitions:
Pathogens are disease-causing microorganisms that can enter our bodies through:
Once inside, they can multiply rapidly and produce toxins that damage cells and make us feel ill.
The body has several lines of defence:
White blood cells are central to both non-specific and specific immunity.
There are several types of white blood cells, each with different roles in protecting the body. The two main categories are phagocytes and lymphocytes.
Phagocytes are white blood cells that can change shape to surround, engulf and digest pathogens in a process called phagocytosis.
How phagocytosis works:
Phagocytes provide a non-specific immune response because they attack any foreign material, not just specific pathogens.
Lymphocytes are responsible for the specific immune response. There are two main types:
B lymphocytes (B cells):
T lymphocytes (T cells):
When a pathogen enters your body, a coordinated immune response is triggered to eliminate the threat.
White blood cells detect the presence of pathogens by recognising proteins on their surface called antigens. Each pathogen has unique antigens that act like a name tag.
B lymphocytes that can recognise the specific antigen are activated. They multiply rapidly and produce antibodies that lock onto the pathogen's antigens.
Antibodies mark pathogens for destruction. They can immobilise pathogens, clump them together, or make them more easily engulfed by phagocytes.
Antibodies (also called immunoglobulins) are Y-shaped proteins produced by B lymphocytes. They are highly specific and will only bind to the antigen that triggered their production.
Antibodies help fight infection in several ways:
Scientists can now produce large quantities of identical antibodies called monoclonal antibodies. These are used in pregnancy tests, cancer treatments and diagnosing diseases. For example, in a pregnancy test, monoclonal antibodies detect the hormone hCG in urine, causing a colour change on the test strip if pregnancy has occurred.
After fighting off an infection, your body remembers how to combat that specific pathogen, providing immunity against future infections by the same pathogen.
When B lymphocytes are activated during an infection, some become memory cells. These remain in the body for many years, sometimes for life. If the same pathogen enters the body again:
This is why you typically only get diseases like chickenpox once in your lifetime.
Vaccines provide artificial active immunity without causing the disease. They contain:
When vaccinated, your immune system responds by:
If you later encounter the real pathogen, your body can mount a rapid response.
Natural immunity: Acquired through exposure to pathogens
Artificial immunity: Acquired through medical intervention
Vaccination programmes have dramatically reduced the incidence of many deadly diseases. When a high percentage of a population is vaccinated, it creates "herd immunity," protecting even those who cannot be vaccinated due to age or medical conditions.
Smallpox was a deadly disease that killed millions of people throughout history. Thanks to a global vaccination programme led by the World Health Organization, smallpox was officially declared eradicated in 1980. This is the only human disease to have been completely eliminated through vaccination, showing the powerful impact of immunisation programmes.
Some pathogens can evade the immune system:
Understanding how white blood cells and immunity work is crucial for developing new treatments and vaccines to combat emerging diseases and antibiotic resistance.
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