Human NKG2D-ligands: cell biology strategies to ensure immune recognition

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• The activating receptor NKG2D is vital for immune surveillance, targeting stressed cells like tumors and virus-infected cells.
• NKG2D ligands, including MIC A/B and ULBPs, are shed into circulation in cancer patients, impairing immune responses.
• While MIC A/B and ULBPs share similarities with MHC molecules and increase under stress, they exhibit distinct biochemical properties and cellular trafficking.

Purpose of the Study:

• To summarize the diversity of NKG2D ligands.
• To explore the evolutionary pressures shaping NKG2D ligand trafficking and shedding.
• To propose a categorization of NKG2D ligands based on biological features for better disease association understanding.

Main Methods:

• Literature review and synthesis of existing data on NKG2D ligands.
• Comparative analysis of the biochemical properties and cell trafficking of MIC A/B and ULBP families.
• Exploration of evolutionary aspects related to ligand diversity and immune evasion.

Main Results:

• Selection pressure has driven diversity in NKG2D ligand trafficking and shedding, but not receptor binding affinity.
• Individual ULBP molecules and MICA/B alleles share functional properties not conserved within their respective families.
• These shared properties suggest convergent evolution for immune recognition and potential targets for pathogen immune evasion.

Conclusions:

• Understanding the diversity of NKG2D ligands is crucial for comprehending their role in immune recognition and disease.
• Categorizing NKG2D ligands by biological features, rather than genetic families, may enhance our understanding of their association with diseases like cancer.
• NKG2D ligand shedding represents a significant immune evasion strategy exploited by pathogens and cancer cells.