Invariant chain cleavage and peptide loading in major histocompatibility complex class II vesicles

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• B lymphocytes present antigens via Major Histocompatibility Complex (MHC) class II molecules.
• MHC class II molecules are synthesized and loaded with peptides in a complex intracellular pathway.

Purpose of the Study:

• To investigate the role of class II-enriched vesicles (CIIV) in the peptide loading of MHC class II molecules.
• To determine if CIIV are a specialized site for the final steps of MHC class II maturation.

Main Methods:

• Utilized the serine protease inhibitor leupeptin to accumulate intermediates in MHC class II transport.
• Analyzed the accumulation of invariant chain fragments and MHC class II alpha beta dimers in CIIV, endosomes, and lysosomes.
• Observed the dissociation of invariant chain fragments and formation of peptide-loaded MHC class II dimers.

Main Results:

• Leupeptin caused accumulation of invariant chain and MHC class II in endosomes and lysosomes.
• Leupeptin enhanced the accumulation of an invariant chain fragment with empty alpha beta dimers in CIIV.
• Observed dissociation of the invariant chain fragment, formation of peptide-loaded alpha beta dimers, and their transport to the cell surface within CIIV.

Conclusions:

• Class II-enriched vesicles (CIIV) are a specialized intracellular site for MHC class II peptide loading.
• CIIV facilitate the final dissociation of invariant chain and loading of antigen-derived peptides onto MHC class II molecules.
• This process occurs distinctly from endosomes and lysosomes, highlighting a novel pathway in antigen presentation.