VMBO Year 2 · HAVO/VWO Years 2–3 · Circulation · Section 3.5

The immune system

Foreign substances and barriers

The body encounters many substances and microorganisms from outside. Some are harmless; pathogens can cause disease.

Barriers such as skin, mucus-lined airways and stomach acid help protect the body. Skin blocks many microorganisms, mucus traps particles, and stomach acid kills many swallowed microbes.

Antigens

If pathogens enter and multiply, an infection can develop. White blood cells and other parts of the immune system help defend the body.

Immune cells recognise molecular features called antigens, which may occur on cells, viruses or other material. Antigens are often proteins, but can be other types of molecules.

Antibodies

Some white blood cells develop into cells producing antibodies. These proteins bind specific antigen features, helping neutralise pathogens or mark them for destruction.

The body can produce many different antibodies. They travel in blood and other body fluids.

Immunity

A first encounter may take time to produce an effective specific response, so illness can occur. Memory cells can remain after an infection or vaccination.

On later exposure, they may respond faster and more strongly. This provides immunity, although protection can vary and may weaken over time.

• Naturally acquired immunity: Develops after exposure to an infection, for example chickenpox.
• Vaccine-induced immunity: Develops after vaccination, without needing to undergo the full disease.

Vaccination

Vaccines expose the immune system to safe forms of pathogen-related information. They may contain weakened or inactivated pathogens, selected components, or instructions for making a component.

The Dutch National Immunisation Programme offers protection against serious diseases such as polio and measles. High vaccination coverage helps limit spread; for measles, a target of about 95% coverage with the recommended doses is widely used.

When too few people are protected, outbreaks become more likely. Reasons for missed vaccinations vary and can include access barriers, concerns or beliefs.

Allergic reactions

An allergy occurs when the immune system responds to a usually harmless substance, such as certain foods or pollen. Symptoms can include itching, rash, swelling or inflammation.

A severe reaction, anaphylaxis, can cause breathing difficulty and dangerously low blood pressure. People at risk may be prescribed an adrenaline auto-injector, such as an EpiPen, as part of their emergency plan.