HLA-A2 molecules in an antigen-processing mutant cell contain signal sequence-derived peptides

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Mutant T2 cells exhibit defects in antigen presentation via human class I (HLA) molecules.
• These defects are linked to impaired transport of antigenic peptides into the endoplasmic reticulum (ER).
• Class I major histocompatibility complex (MHC) molecules require peptide binding for stability and surface expression.

Purpose of the Study:

• To investigate the peptide-binding capabilities of mouse (H-2) and human (HLA) class I molecules in T2 cells.
• To determine if 'empty' class I molecules are unstable or retained in the ER.
• To identify endogenous peptides bound by HLA-A2 molecules in T2 cells.

Main Methods:

• Expression of mouse H-2 and human HLA-A2 in T2 cells.
• Analysis of surface expression and peptide binding of class I molecules.
• Peptide sequencing of bound peptides.

Main Results:

• Surface-expressed HLA-A2 and H-2 molecules in T2 cells are largely peptide-deficient.
• 'Empty' H-2 molecules are stable and expressed on the cell surface.
• HLA-A2 molecules bind a limited set of endogenous peptides, including unusual lengths.
• Identified peptides derived from a signal sequence of IP-30 and an unknown source.

Conclusions:

• 'Empty' mouse class I molecules are stable and not retained in the ER.
• HLA-A2 molecules bind specific endogenous peptides, including signal peptide fragments.
• Peptide generation for HLA-A2 may occur in the cytosol before ER transport.