Peptide binding to mixed isotype Abeta(d)Ealpha(d) class II histocompatibility molecules

Area of Science:

• Immunology
• Molecular Biology
• MHC Class II Research

Background:

• Mixed isotype A beta(d) E alpha(d) molecules show low expression in normal H-2(d) mouse B cells.
• T-cell responses restricted by A beta(d) E alpha(d) occur despite low molecule expression.
• Previous studies highlight T-cell induction with specific peptides and myoglobin in H-2(d) mice.

Purpose of the Study:

• Investigate the peptide-binding behavior of mixed isotype A beta(d) E alpha(d) molecules.
• Determine the affinity and conditions for peptide binding to A beta(d) E alpha(d).
• Explain the basis for unusual T-cell responses restricted by A beta(d) E alpha(d).

Main Methods:

• Purified A beta(d) E alpha(d) molecules were used for peptide-binding assays.
• Binding affinity was assessed for invariant chain peptide (I(1-18)), YL2, FL2, and myoglobin peptides.
• pH dependence of binding was evaluated to mimic endosomal conditions.

Main Results:

• A beta(d) E alpha(d) binds I(1-18) with high affinity, optimally at pH 5, suggesting endosomal preference.
• YL2 and FL2 peptides bind with lower affinity and are selectively restricted to A beta(d) E alpha(d).
• Myoglobin peptides bind to both parental (I-E(d), I-A(d)) and mixed isotype molecules.

Conclusions:

• The binding characteristics of A beta(d) E alpha(d) explain the selective T-cell restriction observed.
• High-affinity T cells responding to low peptide concentrations are likely responsible for unusual responses.
• Peptide binding does not suggest unusually high occupancy of A beta(d) E alpha(d) molecules in vivo.