MAVO Year 4 · Transport and immune defence · Section 13.6

Immune defence

Infection and general defences

An infection occurs when a pathogen enters the body and establishes itself or multiplies. Not every foreign substance is a pathogen. General defences include the skin barrier and its secretions, mucus and cilia, stomach acid, and immune cells that engulf and destroy microbes. Fever is a regulated rise in body temperature during some infections and can support immune responses; infection does not always cause fever.

Specific defence

Antigens are molecular structures recognised by the adaptive immune system. Antibodies, made by plasma cells derived from B lymphocytes, bind specific antigens. They can neutralise particular targets or mark them for other immune processes. Other cells, including T lymphocytes, also contribute to specific defence.

After an immune response, memory cells can remain. Along with persisting antibodies, they can produce a faster response on later exposure. Protection may reduce infection or severe illness rather than guarantee that reinfection is impossible, and its duration varies.

Natural and vaccine-induced immunity

Naturally acquired active immunity develops after exposure to an infection. Vaccine-induced immunity develops after the immune system encounters a vaccine. Vaccines may contain weakened or inactivated pathogens, selected components or instructions for producing an antigen. They aim to generate protection without the risks of the corresponding disease, although temporary side effects can occur.

Active and passive immunisation

In active immunisation, the person's own immune system responds and can form memory. In passive immunisation, ready-made antibodies provide more immediate but usually temporary protection; they do not normally create lasting immune memory themselves.

Babies receive maternal antibodies through the placenta before birth. Breast milk provides antibodies and other protective factors, especially at mucosal surfaces. These effects do not replace the baby's developing immune system or recommended vaccinations.

Vaccination in animals

Pets and farm animals can also be vaccinated, for example against particular poultry diseases or Q fever in relevant livestock. Veterinary programmes depend on the species, disease and local rules. Vaccination can reduce disease and spread but does not automatically prevent every outbreak.

Allergies and hay fever

An allergy is an immune response to a substance that is usually harmless, such as pollen, some foods or dust-mite material. Symptoms can include itching, rashes, sneezing or breathing problems. Hay fever is an allergy to airborne pollen, commonly affecting the nose and eyes.