An endosome is a membrane-bound compartment inside eukaryotic cells that plays a key role in sorting and transporting internalized material. It's part of the endocytic pathway, which is how cells take in molecules from their surroundings.

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### 🧬 What does an endosome do?

Endosomes are responsible for:

- Sorting internalized molecules (like nutrients, receptors, and pathogens) - Transporting cargo to different destinations:

1. Back to the plasma membrane (recycling)
2. To the Golgi apparatus
3. To lysosomes for degradation

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### 📦 Types of Endosomes

1. Early endosomes

1. First station after internalization
2. Mildly acidic
3. Decide whether cargo gets recycled or degraded

2. Late endosomes

1. More acidic
2. Fuse with lysosomes for degradation

3. Recycling endosomes

1. Return cargo (like receptors) back to the plasma membrane

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### 🦠 Role in Immunity

Endosomes are crucial in nucleic acid-mediated signaling, especially:

- TLR3, TLR7, TLR8, and TLR9 are located in endosomal membranes - They detect viral RNA or DNA inside endosomes, triggering immune responses

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### 🧪 Clinical relevance

- Pathogens (like viruses) may exploit endosomes to enter cells - Dysregulated endosomal trafficking is linked to neurodegenerative diseases and autoimmunity - Therapeutic delivery systems (e.g., mRNA vaccines) often target endosomal uptake