The MHC Class II Antigen-Processing and Presentation Pathway Is Dysregulated in Type 1 Diabetes

Area of Science:

• Immunology
• Molecular Biology
• Endocrinology

Background:

• Peptide loading onto MHC class II (MHCII) molecules is crucial for immune response and is regulated by HLA-DM (DM) and HLA-DO (DO).
• MHCII-peptide presentation is abnormal in type 1 diabetes (T1D), contributing to immune tolerance breakdown.
• Previous studies lacked direct measurements of MHCII pathway activity in T1D patients.

Purpose of the Study:

• To directly measure and analyze the activity of the MHCII antigen-processing pathway in T1D patients.
• To investigate the levels of MHCII, MHCII-CLIP, DM, and DO in immune cells of T1D patients and healthy controls.

Main Methods:

• Flow cytometry was used to quantify MHCII, MHCII-CLIP, DM, and DO levels in peripheral blood B cells, dendritic cells, and monocytes.
• Gene expression profiling of peripheral blood mononuclear cell (PBMC) RNA was performed.
• Analysis included 99 T1D patients and 97 healthy controls.

Main Results:

• MHCII levels were comparable between T1D patients and controls across all analyzed cell types.
• MHCII-CLIP levels were significantly elevated (up to 3.4-fold in B cells) in all APC subsets of T1D patients.
• DM and DO levels were unexpectedly similar in T1D patients and controls, despite increased MHCII-CLIP.
• Elevated DMB mRNA in T1D patients with residual C-peptide correlated with increased DM protein in B cells and dendritic cells.
• Increased DO levels were also observed in T1D patients with residual C-peptide.

Conclusions:

• The MHCII antigen-processing pathway is significantly dysregulated in T1D patients.
• Elevated MHCII-CLIP levels suggest impaired CLIP release or MHCII stabilization.
• Differential regulation of the MHCII pathway may be associated with residual C-peptide levels in T1D individuals.