Due to unknown or genetic reasons, immune system attacks on its own cell, it is called as :-

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about a condition where the immune system attacks its own cells due to unknown or genetic reasons.

2. **Defining Autoimmunity**: The term used to describe the immune system attacking its own cells is "autoimmunity." This occurs when the body's immune system mistakenly identifies its own cells as foreign and mounts an immune response against them.

3. **Causes of Autoimmunity**:
- **Genetic Factors**: Certain genetic mutations can predispose individuals to autoimmune diseases.
- **Environmental Factors**: These may include infections, drugs, or chemical agents that can trigger an autoimmune response.
- **Sex-Related Factors**: Some autoimmune diseases show a significant difference in prevalence between males and females, indicating that sex may play a role in susceptibility.

4. **Examples of Autoimmune Diseases**: Some common autoimmune diseases include:
- Rheumatoid arthritis
- Systemic lupus erythematosus
- Type 1 diabetes mellitus
- Multiple sclerosis

5. **Conclusion**: Based on the definition and the causes discussed, the answer to the question is "autoimmunity."

**Final Answer**: Autoimmunity

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