What is auto-immune disease? Give one example.

Explanation

### Step-by-Step Solution:

1. **Definition of Autoimmune Disease**:
- Autoimmune diseases are disorders where the immune system mistakenly attacks and destroys the body’s own cells. Normally, the immune system protects the body from foreign invaders like bacteria and viruses. However, in autoimmune diseases, the immune system fails to recognize its own cells and treats them as threats.

2. **Mechanism of Autoimmune Diseases**:
- In autoimmune diseases, the body’s immune cells, which usually function to protect against pathogens, begin to target and destroy healthy cells. This occurs because the immune system identifies these cells as foreign due to a malfunction in its recognition system.

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