Antigen three-dimensional structure guides the processing and presentation of helper T-cell epitopes

Area of Science:

• Immunology
• Structural Biology
• Protein Chemistry

Background:

• Antigen three-dimensional structure is crucial for CD4(+) T-cell epitope presentation.
• Proteolytic enzyme access and MHC class II binding are modulated by antigen structure.
• Mobile loops in heat shock protein 10 (Hsp10) are linked to T-cell epitope immunodominance.

Purpose of the Study:

• To investigate how antigen structure, specifically mobile loops, affects protease sensitivity and T-cell epitope presentation.
• To analyze the impact of mobile loop modifications on epitope processing and presentation by MHC class II molecules.

Main Methods:

• Construction and analysis of bacteriophage T4 Hsp10 (T4Hsp10) variants with altered mobile loop sequences.
• Assessment of protease sensitivity of wild-type and variant T4Hsp10 proteins.
• Evaluation of T-cell epitope presentation using MHC class II binding assays.

Main Results:

• Variant T4Hsp10 proteins maintained native-like structure and mobile loop protease sensitivity.
• Mobile loop modifications differentially affected the presentation of protease-independent and protease-dependent epitopes.
• A protease-independent epitope was located within the mobile loop, while a protease-dependent epitope was adjacent to it.

Conclusions:

• The three-dimensional structure of antigens, particularly mobile loops, plays a key role in regulating T-cell epitope presentation.
• Proteolytic processing of mobile loops can unlock antigen structure, facilitating the presentation of specific epitopes.
• These findings provide insights into the mechanisms of antigen processing and T-cell activation.