Expression of a functional chimeric Ig-MHC class II protein

Area of Science:

• Immunology
• Molecular Biology
• Protein Engineering

Background:

• Major histocompatibility complex (MHC) class II molecules present antigens to T helper cells.
• Antibody variable (V) regions provide specific antigen-binding capabilities.
• Engineering hybrid molecules can combine functions of different protein families.

Purpose of the Study:

• To generate a chimeric protein molecule by fusing MHC class II I-E alpha and beta chains with antibody V regions.
• To investigate the expression, stability, and functional properties of the resulting hybrid molecule.
• To assess the utility of this hybrid molecule for studying MHC class II-mediated functions.

Main Methods:

• Constructed expression vectors with rearranged antibody V region gene segments fused to MHC class II I-E alpha and beta chain genes.
• Transfected cells with both hybrid genes and confirmed surface expression of the chimeric protein.
• Utilized anti-idiotypic monoclonal antibody (mAb) 20-46 and human soluble CD4 to characterize the chimeric molecule's binding properties.
• Performed immunoprecipitation with anti-mouse IgG antiserum to confirm molecular mass.

Main Results:

• Successfully generated a stable chimeric protein expressed on the cell surface.
• The chimeric molecule exhibited the idiotype of the anti-human CD4 mAb MT310 and bound to anti-idiotypic mAb 20-46.
• Human soluble CD4 bound to the transfected cells, confirming the antibody-like antigen-binding capacity.
• The hybrid molecule demonstrated correct MHC class II chain assembly and cell surface transport.

Conclusions:

• The generated hybrid MHC class II-antibody V region molecule retains essential properties of both parent molecules.
• This engineered protein possesses specific, non-MHC-restricted binding capacity.
• Such hybrid molecules offer a valuable tool for exploring MHC class II-mediated effector functions, including T cell repertoire selection in transgenic models.