# The Immune System and Vaccination
The body has multiple lines of defence against pathogens. If pathogens get past physical barriers, the immune system attacks them using white blood cells.
1. Non-Specific Defences (First Line)
| Defence | How It Works |
|---|---|
| Skin | Physical barrier |
| Nose hairs and mucus | Trap particles |
| Tears and saliva | Contain lysozyme (enzyme that kills bacteria) |
| Stomach acid (HCl) | Kills pathogens in food |
| Cilia | Sweep mucus with trapped pathogens out of airways |
2. White Blood Cell Defences
Phagocytosis
- Phagocytes surround, engulf, and digest pathogens
- Non-specific (attack any pathogen)
Antibody Production
- Lymphocytes recognise specific antigens on pathogens
- Produce antibodies that lock onto antigens
- Antibodies are specific to each pathogen
- Memory cells remain for rapid response next time
Antitoxin Production
- Lymphocytes produce antitoxins that neutralise toxins produced by bacteria
3. Vaccination
- Inject dead/inactive pathogen (or part of it)
- White blood cells detect antigens and produce antibodies
- Memory cells are formed
- If the real pathogen enters: rapid antibody production → pathogen destroyed before disease develops
Herd Immunity
If enough people are vaccinated, the pathogen can't spread easily, protecting unvaccinated individuals.
4. Drugs
Antibiotics
- Kill bacteria or prevent them from growing
- Do NOT work on viruses
- Example: penicillin
- Antibiotic resistance: overuse of antibiotics → bacteria evolve resistance (e.g. MRSA)
Painkillers
- Relieve symptoms (pain) but don't kill pathogens
- Examples: paracetamol, ibuprofen
Antivirals
- Slow down viral replication (hard to develop as viruses live inside cells)
5. Drug Development
- Discovery: laboratory testing (in vitro)
- Pre-clinical: animal testing for safety and efficacy
- Clinical trials: human volunteers (Phase 1-3)
- Double-blind trials: neither patient nor doctor knows who has drug vs placebo
- Peer review and approval
6. Practice Questions
- Describe three non-specific defences of the body.
- Explain how vaccination produces immunity.
- Why don't antibiotics work on viruses?
- What is the role of memory cells?
- Explain why antibiotic resistance is a problem.
Want to check your answers and get step-by-step solutions?
Summary
- First line: skin, mucus, acid, cilia
- WBC defence: phagocytosis, antibodies, antitoxins
- Vaccination: dead pathogen → antibodies → memory cells → rapid future response
- Antibiotics kill bacteria, not viruses
- Antibiotic resistance from overuse → MRSA