Define auto-immune diseases. Give two examples.

Explanation

### Step-by-Step Solution:

1. **Definition of Autoimmune Diseases**:
- Autoimmune diseases are conditions in which the body's immune system mistakenly attacks its own cells and tissues. Normally, the immune system is designed to protect the body from foreign pathogens (like bacteria and viruses). However, in autoimmune diseases, the immune cells fail to distinguish between the body's own healthy cells (self) and foreign invaders (non-self), leading to damage to the body's own tissues.

2. **Mechanism of Autoimmune Diseases**:
- In a healthy immune response, the immune system identifies and neutralizes pathogens while preserving the body's own cells. In autoimmune diseases, this process is disrupted due to abnormal physiological conditions, causing the immune system to attack the body’s own cells.

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