The nonconventional MHC class II molecule DM governs diabetes susceptibility in NOD mice.

Marc A J Morgan,Pari S S Muller,Anne Cooke,Elizabeth J Robertson,Arne Mould,Jennifer Nichols,Stephen A Newland,Elizabeth K Bikoff,Susan Kovats

doi:10.1371/journal.pone.0056738

Abstract

The spontaneous destruction of insulin producing pancreatic beta cells in non-obese diabetic (NOD) mice provides a valuable model of type 1 diabetes. As in humans, disease susceptibility is controlled by the classical MHC class II genes that guide CD4+ T cell responses to self and foreign antigens. It has long been suspected that the dedicated class II chaperone designated HLA-DM in humans or H-2M in mice also makes an important contribution, but due to tight linkage within the MHC, a possible role played by DM peptide editing has not been previously tested by conventional genetic approaches. Here we exploited newly established germ-line competent NOD ES cells to engineer a loss of function allele. DM deficient NOD mice display defective class II peptide occupancy and surface expression, and are completely protected against type 1 diabetes. Interestingly the mutation results in increased proportional representation of CD4+Foxp3+ regulatory T cells and the absence of pathogenic CD4+ T effectors. Overall, this striking phenotype establishes that DM-mediated peptide selection plays an essential role in the development of autoimmune diabetes in NOD mice.

Highlights

In mice and humans, susceptibility to type 1 diabetes is predominantly controlled by the classical MHC class II loci responsible for positive and negative selection of CD4+ T cell clones during thymic development [1,2,3]
The non-obese diabetic (NOD) I-Ag7 and human HLA-DQ8 molecules, strongly associated with diabetes, both lack a conserved aspartic acid at position b 57 that normally pairs with the conserved arginine a 76 [4,5,6]
The loss of this salt bridge widens the P-9 pocket and splenocytes from B10.BR or NOD mouse strains were cultured for 5 hrs at 37uC with biotin-conjugated peptides or medium alone as indicated, stained with FITC-labelled avidin, and analysed by FACS

Summary

Introduction

Susceptibility to type 1 diabetes is predominantly controlled by the classical MHC class II loci responsible for positive and negative selection of CD4+ T cell clones during thymic development [1,2,3]. The diabetes-associated NOD I-Ag7 molecule shares with predisposing human HLA-DQ alleles exceptional substitutions at the highly conserved Pro 56 and Asp 57 residues. This structural change creates an unusually wide peptide-binding groove [4,5,6]. Besides highly polymorphic MHC class II subunits, surface display of diverse peptide ligands depends on the combined activities of two dedicated chaperones, namely the conserved Invariant (Ii) chain and the nonconventional class II molecule DM required at distinct stages during maturation and export. Susceptibility to DM editing was recently shown to modulate insulin-specific T cell reactivity in mice [12]

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Results

Conclusion