Immunity
🧠 Immunity — Definition and Types
Definition: Immunity is the ability of the body to resist and fight against infections, diseases, or harmful foreign substances such as bacteria, viruses, and toxins. It involves specialized cells and organs that recognize and destroy invading agents.
🔹 Main Categories of Immunity
- Innate (Natural) Immunity
- Acquired (Adaptive) Immunity
1️⃣ Innate (Natural) Immunity
This is the first line of defense present from birth. It is non-specific and responds immediately to all pathogens in a similar way.
- Features: Present from birth, immediate action, no memory.
- Components: Skin, mucous membranes, stomach acid, tears, phagocytic cells (neutrophils, macrophages).
- Examples: Skin preventing bacterial entry; phagocytes engulfing microbes.
2️⃣ Acquired (Adaptive) Immunity
Develops after exposure to specific pathogens. It is specific and has memory, which provides stronger responses upon re-infection.
Acquired immunity is divided into Active and Passive forms, each of which can be Natural or Artificial.
A. Active Immunity
The body produces its own antibodies after exposure to an antigen (infection or vaccination). It provides long-term protection.
| Type | Description | Example |
|---|---|---|
| Natural Active | Antibodies formed after natural infection | After recovering from measles |
| Artificial Active | Antibodies formed after vaccination | After receiving polio or COVID-19 vaccine |
B. Passive Immunity
Occurs when ready-made antibodies are transferred into the body. It provides immediate but short-term protection.
| Type | Description | Example |
|---|---|---|
| Natural Passive | Antibodies received naturally | From mother to baby via placenta or breast milk |
| Artificial Passive | Ready-made antibodies given artificially | Anti-tetanus serum, Rabies immunoglobulin |
🧩 Comparison of Active and Passive Immunity
| Feature | Active Immunity | Passive Immunity |
|---|---|---|
| Antibody Source | Produced by own body | Received from outside |
| Onset | Slow | Immediate |
| Duration | Long-lasting | Short-lived |
| Memory | Present | Absent |
| Example | Vaccination | Anti-tetanus injection |
- Active Immunity: Body produces its own antibodies → Long-term protection.
- Passive Immunity: Ready-made antibodies given → Immediate but short-lived protection.
Learn | Practice | Pass