An autoantigenic T cell epitope forms unstable complexes with class II MHC: a novel route for escape from tolerance...

Area of Science:

• Immunology
• Molecular Biology
• Autoimmunity

Background:

• The peptide rAc1-11 is a key T cell epitope of rat myelin basic protein (MBP) in H-2u mice.
• Residue 4 of rAc1-11 is critical for binding to the class II molecule I-A.
• Understanding peptide-MHC interactions is crucial for autoimmune disease research.

Purpose of the Study:

• To investigate the impact of amino acid substitutions at position 4 of rAc1-11 on I-A binding and T cell stimulation.
• To determine the stability and fate of peptide-MHC class II complexes on antigen-presenting cells (APCs).
• To explore the implications for tolerance induction and autoimmune responses.

Main Methods:

• Construction and testing of rAc1-11 peptide analogues with substitutions at position 4.
• Assessment of T cell hybridoma stimulation by viable APCs presenting peptide-MHC complexes.
• Measurement of the half-life (t 1/2) of peptide-I-A complexes on APC surfaces.

Main Results:

• The analogue rAc1-11[4A] formed complexes with I-A that were rapidly lost from APC surfaces (t 1/2 ≈ 10 min).
• Complex loss was not due to shedding or intracellular recycling.
• The analogue rAc1-11[4Y] showed stable binding (t 1/2 > 4 h), while wild-type rAc1-11 bound transiently, undetectable on APCs.
• Murine MBP homologous epitope also showed minimal affinity for I-A.

Conclusions:

• Peptide binding affinity to I-A significantly influences the stability of peptide-MHC complexes on APCs.
• Transient binding of MBP epitopes to I-A may represent a mechanism for escaping tolerance induction.
• These findings suggest novel strategies for modulating T cell responses in autoimmune diseases like experimental autoimmune encephalomyelitis (EAE).