Immunity: Your Body's Defence System
Innate & Acquired Immunity, Vaccination, and Immune Memory
Recall from our previous lesson: We learned that blood contains white blood cells (leukocytes) that protect the body from infection. Today, we dive deep into how these defences actually work — and why vaccines are so powerful.
🛡️ Section 1: The Two Arms of the Immune System
Your body has two major defence systems that work together like a castle's defences. Think of it this way: the castle walls and moat stop any invader (innate immunity), while specially trained knights target specific enemies (adaptive/acquired immunity).
⚔️ Innate (Inborn) Immunity
Innate immunity is the defence you are born with. It is an antigen-nonspecific mechanism that responds immediately or within hours of exposure to almost any microbe.
Key Features:
- Fast: Acts within minutes to hours
- Non-specific: Fights ALL invaders the same way
- No memory: Does not remember past infections
- Present from birth
Examples of Innate Defences:
| Defence | How It Works |
|---|---|
| Skin | Physical barrier — blocks pathogens from entering |
| Mucous membranes | Trap microbes in nose, throat, lungs |
| Phagocytes | White blood cells that "eat" invaders |
| Inflammation | Redness & swelling bring more immune cells to the area |
| Fever | Raised body temperature slows pathogen growth |
🎯 Adaptive (Acquired) Immunity
Adaptive immunity refers to antigen-specific defence mechanisms that take several days to become protective and are designed to react with and remove a specific antigen. This is the immunity you develop throughout life.
Key Features:
- Slower initially: Takes days to weeks on first exposure
- Highly specific: Targets one particular pathogen
- Has memory: Remembers pathogens for future defence
- Develops over your lifetime
Two Branches:
| Branch | Key Player | Action |
|---|---|---|
| Humoral | B-lymphocytes (B cells) | Produce antibodies that neutralise pathogens |
| Cell-mediated | T-lymphocytes (T cells) | Directly destroy infected cells |