HLA-DP^84Gly constitutively presents endogenous peptides generated by the class I antigen processing pathway

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Classical antigen processing presents peptides via MHC class I (endogenous) and MHC class II (exogenous) pathways.
• HLA-DP molecules are a subset of MHC class II molecules with distinct processing and presentation characteristics.

Purpose of the Study:

• To investigate the antigen processing and presentation capabilities of HLA-DP molecules encoding Gly84 (DP^84Gly).
• To determine if DP^84Gly utilizes classical MHC class I or class II pathways for peptide presentation.

Main Methods:

• Analysis of invariant chain (Ii) binding to DP^84Gly, focusing on the CLIP region.
• Investigation of peptide presentation from endogenous sources by DP^84Gly.
• Tracking the cellular transport of DP^84Gly from the endoplasmic reticulum (ER) to endosomal/lysosomal compartments.
• Assessing the role of the transporter associated with antigen processing (TAP) in DP^84Gly peptide loading.

Main Results:

• DP^84Gly constitutively presents endogenous peptides, a function typically associated with MHC class I molecules.
• DP^84Gly does not bind or present the class II-associated invariant chain peptide (CLIP).
• Invariant chain (Ii) facilitates DP^84Gly transport via non-CLIP regions in a pH-sensitive manner, independent of CLIP binding.
• DP^84Gly presents peptides processed by the proteasome and transported by TAP, similar to MHC class I molecules.
• DP^84Gly, found in humans and common chimpanzees, uniquely integrates both endogenous and exogenous antigen processing pathways.

Conclusions:

• DP^84Gly exhibits a unique dual-pathway antigen presentation mechanism, utilizing both MHC class I and II processing routes.
• This distinct mechanism allows DP^84Gy to present peptides derived from both intracellular and extracellular sources.
• The findings reveal a novel aspect of immune surveillance involving HLA-DP molecules specific to humans and chimpanzees.