Immune System Key Concepts: Pathogens, Defence, Vaccines, Resistance

Pathogen

A microorganism that causes disease.

Microbe

Any microscopic organism.

Difference between microbe and pathogen

A pathogen is a specific type of microbe that causes disease. (Not all microbes are pathogens).

Four main types of pathogens

1. Bacterium (e.g., Strep throat, Tuberculosis) 2. Virus (e.g., Flu, COVID-19, Measles) 3. Fungus (e.g., Athlete's foot) 4. Protist (e.g., Malaria)

Infectious disease

A disease caused by a pathogen that can be spread.

Contagious disease

An infectious disease that spreads easily from person to person (e.g., measles, whooping cough).

Non-infectious disease

A disease not caused by a pathogen (e.g., diabetes, asthma, cancer).

How can infectious diseases spread?

Direct contact, airborne droplets (coughing/sneezing), contaminated surfaces, bodily fluids, vectors (e.g., mosquitoes).

1st Line of Defence

To prevent pathogens from entering the body.

Physical barriers

Barriers that block or trap pathogens. Examples: Skin, mucus, cilia.

Chemical barriers

Barriers that kill pathogens. Examples: Stomach acid, enzymes in tears and saliva.

2nd Line of Defence

To limit pathogen growth inside the body. It is a non-specific (general) response.

Three main responses of the 2nd Line of Defence

1. Fever: High body temperature slows down/kills pathogens. 2. Inflammation: Swelling, redness, and heat bring extra blood and white blood cells to the area. 3. Phagocytosis: White blood cells called phagocytes engulf and digest pathogens.

3rd Line of Defence

To target specific pathogens and create long-term immunity. It is a specific (adaptive) response.

Key cells of the 3rd Line of Defence

B Cells: Produce antibodies. Antibodies: Proteins that identify and bind to a specific pathogen. Memory Cells: 'Remember' the pathogen for a faster, stronger response in the future.

Immunity

The body's ability to protect itself from a specific disease.

Similarity between 1st and 2nd Lines of Defence

Both are non-specific (act against all pathogens the same way).

What is a vaccine?

A substance containing a dead/weakened pathogen or part of a pathogen that trains the immune system.

How do vaccines work?

They trigger the 3rd Line of Defence. B cells produce antibodies and, crucially, memory cells, without causing the disease. This provides long-term immunity.

What is herd immunity?

The protection offered to a community when a high percentage of the population (>85%) is vaccinated. This makes it hard for the disease to spread, protecting those who can't be vaccinated (e.g., babies, immunocompromised).

Why is herd immunity important?

It protects vulnerable people who cannot get vaccinated.

What is waning immunity?

When immunity from a vaccine or infection decreases over time, making booster shots necessary.

What do antibiotics treat?

Bacterial infections only. They are useless against viruses (like the flu or COVID-19).

What is antibiotic resistance?

When bacteria change and evolve, making antibiotics ineffective against them.

What causes antibiotic resistance?

The overuse and misuse of antibiotics (e.g., not finishing a prescription, using them for viral infections).

What pathogen causes whooping cough (pertussis)?

The bacterium Bordetella pertussis.

Why are cases of whooping cough rising? (Multiple Factors)

1. Cyclical Nature: The disease naturally peaks every 2-5 years. 2. Waning Immunity: Protection from the vaccine decreases over time. 3. Lower Vaccination Rates: Anti-vaccine sentiment and disrupted health services have reduced coverage. 4. Post-COVID Effect: Lockdowns reduced natural immunity to many diseases.

How can people protect themselves from whooping cough?

Vaccination. The article emphasizes it is a safe and highly effective way to prevent severe illness.

Why is vaccinating during pregnancy important?

It passes antibodies from the mother to the baby, protecting the infant before they are old enough to be vaccinated themselves (at 6 weeks).