Your body produces potential cancer cells every day; how does the immune system track them down?
The Core Framework: The Three-Signal Model of Immune Surveillance
| Core Dimension | Explanation |
|---|---|
| Missing Self Signal | Cancerous cells downregulate MHC-I → NK cells recognize the missing "self" signal → immediately attack and clear. |
| Stress Signal (NKG2D) | DNA damage and cellular stress → NKG2D ligands (MICA/MICB/ULBP) appear on cell surfaces → NK cells are activated to attack. |
| Neoantigen Signal (MHC-I) | Mutated proteins produced by cancer cells are presented via MHC-I → CD8+ T cells recognize neoantigens → precise, specific killing. |
| Tumor Evasion Strategies | Downregulating MHC-I (hiding from T cells) + expressing PD-L1 (stepping on the brakes for T cells) + secreting TGF-β (building an immunosuppressive microenvironment). |
Diagram: Core Mechanism
DNA replication errors during normal cell division / Environmental mutagens
↓(Generation of early cancerous cells)
Abnormal signals: MHC-I downregulation + Appearance of NKG2D ligands + Neoantigen presentation
↓
NK cells (Rapid response) + CD8+ T cells (Precise killing)
↓(In most cases)
Successful clearance →You feel absolutely nothing
↓(If evasion occurs)
Tumor microenvironment forms →Immunosuppression →Tumor growth
