NOD2/CARD15 

🦠 Bacterial infection

        ↓

🧱 Muramyl Dipeptide (MDP) 

   (from bacterial peptidoglycan)

        ↓

🏠 Enters host cell cytoplasm (e.g., gut epithelial cell)

        ↓

🧬 NOD2 detects MDP (in cytoplasm)

        ↓

🔗 NOD2 oligomerizes + recruits RIP2 kinase (RICK)

        ↓

🔥 Activates NF-κB and MAPK pathways

        ↓

📢 Cytokine production (TNF-α, IL-6, IL-1β)

        ↓

🛡️ Inflammation + Antimicrobial defenses