The Immune System and VaccinationAQA GCSE Biology: Revision notes

The body has non-specific defence systems that stop pathogens entering in the first place:

• Skin — acts as a physical barrier and secretes antimicrobial substances
• Nose — hairs and mucus trap particles and pathogens
• Trachea and bronchi — lined with cilia and mucus, which trap and move pathogens away from the lungs
• Stomach — hydrochloric acid kills many pathogens swallowed with food or drink

If a pathogen enters the body, white blood cells help defend against it in three main ways:

1. Phagocytosis — white blood cells engulf and digest pathogens
2. Antibody production — white blood cells produce antibodies specific to the antigens on a pathogen's surface, which help destroy it
3. Antitoxin production — white blood cells produce antitoxins that neutralise toxins produced by pathogens

Vaccination involves introducing small quantities of dead or inactive forms of a pathogen (or parts of it) into the body.

• This stimulates white blood cells to produce antibodies specific to that pathogen, without causing disease
• If the same live pathogen enters the body later, white blood cells can respond quickly, producing the correct antibodies fast enough to destroy the pathogen before it causes illness
• If a large proportion of a population is vaccinated, the spread of the pathogen is greatly reduced, protecting even people who are not immune (herd immunity)

Monoclonal antibodies are identical antibodies produced from a single clone of cells, all targeting one specific antigen:

1. Mouse lymphocytes are stimulated to produce a specific antibody
2. These lymphocytes are fused with tumour cells to create hybridoma cells
3. Hybridoma cells divide rapidly and continue producing the antibody
4. Large quantities of the antibody are collected and purified

Because each monoclonal antibody binds to just one antigen, they can be used to target very specific molecules or cells in the body.

• Diagnosis — e.g. pregnancy tests detect a specific hormone using monoclonal antibodies
• Measuring/detecting — measuring hormone levels or detecting pathogens in the laboratory
• Research — locating specific molecules in cells or tissues using fluorescent dyes attached to the antibody
• Treating cancer — a monoclonal antibody can carry a radioactive substance, toxic drug, or other chemical directly to cancer cells, stopping their growth without harming healthy cells