Research background
Insulin and its precursor are among the best-documented autoantigens in type 1 diabetes. The preproinsulin signal peptide is of particular interest because signal-peptide-derived fragments can enter class I presentation pathways by routes that differ from the conventional proteasomal pathway, and because HLA-A*24:02 is recognized as a susceptibility allele in several populations. LWMRLLPLL corresponds to residues 3 to 11 of preproinsulin and is commonly designated PPI3-11.
Work published in Diabetes reported that circulating CD8+ T cells specific for this HLA-A24-restricted signal-peptide epitope are expanded around the onset of type 1 diabetes and are capable of killing beta cells, linking the specificity directly to islet pathology rather than to peripheral reactivity alone. Related studies of autoreactive preproinsulin-specific CD8+ T cells found that beta-cell killing proceeds predominantly through granule-mediated mechanisms, with potency scaling with T-cell receptor avidity, and analyses of T cells recovered from human islets have confirmed strong preproinsulin reactivity in donors with the disease.
Dolton and colleagues subsequently used this peptide as the index antigen in a detailed analysis of the diabetes-derived 4C6 T-cell receptor. Surface plasmon resonance gave a dissociation constant of 129.2 micromolar for 4C6 binding to HLA-A*24:02 presenting LWMRLLPLL, a weak interaction characteristic of autoreactive receptors that have escaped thymic deletion and one that makes stable complexes hard to obtain. The authors nonetheless determined a 4C6-HLA-A*24:02-LWMRLLPLL structure at 2.48 angstrom resolution, using crystals seeded from a complex formed with a higher-affinity superagonist peptide. Combinatorial peptide library screening from the same receptor subsequently led to bacterial peptides recognized far more potently than the natural self sequence, work that has been discussed as evidence for microbial mimicry contributing to the autoreactive response.
LT9748 provides the natural preproinsulin register as a defined comparator for the superagonist and bacterial peptides characterized alongside it (see LT9749, LT9750 and LT9751). The peptide is a research reagent; the studies cited describe mechanism in experimental systems and make no claim about diagnosis or treatment.
Research applications
- Assembly of HLA-A*24:02 multimers for detection of preproinsulin-specific CD8+ T cells
- Surface plasmon resonance measurement of T-cell receptor affinity for a weakly bound self peptide-MHC ligand
- Index antigen for combinatorial peptide library screening and mimotope or superagonist comparison
- Cytotoxicity and granule-release assays using beta cell or surrogate target lines
- Crystallization of receptor-peptide-MHC complexes, including seeding strategies with higher-affinity analogues
- Frequency monitoring of autoreactive CD8+ T-cell populations in HLA-A*24:02-positive cohorts
- Antigen-processing studies of signal-peptide-derived class I ligands
References
- Dolton G, Bulek A, Wall A, et al. HLA A*24:02-restricted T cell receptors cross-recognize bacterial and preproinsulin peptides in type 1 diabetes. Journal of Clinical Investigation (2024) 134:e164535. doi:10.1172/JCI164535
- Circulating preproinsulin signal peptide-specific CD8 T cells restricted by the susceptibility molecule HLA-A24 are expanded at onset of type 1 diabetes and kill beta cells. Diabetes (2012) 61:1752-1759. Diabetes 2012;61:1752
- Human beta-cell killing by autoreactive preproinsulin-specific CD8 T cells is predominantly granule-mediated with the potency dependent upon T-cell receptor avidity. Diabetes (2013) 62:205-213. Diabetes 2013;62:205
- Human islet T cells are highly reactive to preproinsulin in type 1 diabetes. PNAS (2021) 118:e2107208118. doi:10.1073/pnas.2107208118
- Microbial mimics supersize the pathogenic self-response. Journal of Clinical Investigation (2024), commentary. JCI 2024 commentary
The 4C6 cross-reactivity panel and related peptides
For research use only. Not for use in diagnostic or therapeutic procedures, or for human or veterinary use.
