**Autoimmunity** is a condition in which the **immune system mistakenly attacks the body’s own healthy tissues**, thinking they are foreign invaders like viruses or bacteria. This leads to **chronic inflammation**, **tissue damage**, and a wide variety of **autoimmune diseases**.

---

### 🧬 How does autoimmunity develop?

Under normal circumstances, the immune system has mechanisms of **self-tolerance**, meaning it can distinguish between "self" and "non-self." In autoimmunity, this tolerance is **broken**, and immune cells begin to target the body’s own antigens (self-antigens).

Key mechanisms include:

- **Loss of central tolerance** (in thymus or bone marrow)
- **Defects in peripheral tolerance** (failure to suppress rogue immune cells)
- **Molecular mimicry** (pathogens resemble self-proteins)
- **Epitope spreading** (initial immune attack expands to other self-antigens)
- **Aberrant activation of nucleic acid sensors**, like **TLRs or cGAS**, leading to inappropriate immune signaling

---

### 🔥 What happens in autoimmune diseases?

- **Autoantibodies** and **autoreactive T cells** target specific organs or systems
- Chronic **inflammation** and **tissue destruction**
- Often **cyclical flares** and remissions

Examples of autoimmune diseases:
- **Systemic lupus erythematosus (SLE)** – affects skin, kidneys, joints, and brain
- **Rheumatoid arthritis** – joints
- **Type 1 diabetes** – pancreas (β-cells)
- **Multiple sclerosis** – central nervous system (myelin)
- **Hashimoto's thyroiditis** – thyroid gland

---

### 🧪 Biomarkers and Diagnosis

- **Autoantibodies** (e.g., ANA in lupus, anti-TPO in Hashimoto’s)
- Elevated **cytokines** (like IFN-α, IL-6)
- Imaging and **organ-specific tests**
  
---

### 💊 Treatment Approaches

- **Immunosuppressants** (e.g., corticosteroids, methotrexate)
- **Biologics** (e.g., TNF inhibitors, anti-IL-6, anti-CD20)
- **Targeted therapies** (e.g., JAK inhibitors, cGAS-STING inhibitors in trials)
- **Plasmapheresis** (in severe cases)
  
---

### 🧠 Take-home message

Autoimmunity is a **malfunction of immune self-recognition**, leading to **inflammatory disease**. While once considered incurable, modern therapies are increasingly **targeted** and **personalized**, offering better control and improved quality of life for patients.