Distant interactions between dimorphisms in HLA-DR4 radically affect recognition of defined peptides by a specific T...

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Human Leukocyte Antigen (HLA) class II molecules present peptides to T cells.
• Amino acid variations (dimorphisms) in HLA class II alleles can influence peptide binding and T cell recognition.
• The functional impact of these dimorphisms, individually or in combination, is not fully understood.

Purpose of the Study:

• To investigate the functional effects of specific Human Leukocyte Antigen (HLA) class II dimorphisms on peptide presentation.
• To determine whether these effects are context-dependent, considering natural combinations of substitutions.
• To assess the impact of these variations on T cell recognition.

Main Methods:

• Utilized six subtypes of HLA-DR4 differing by single substitutions at key sites (86Gly/Val, 57Asp/Ser, 71Arg/Lys).
• Assessed peptide presentation to a specific T cell clone with broad cross-restrictions.
• Analyzed the effects of substitutions in isolation and in their natural context.

Main Results:

• The 86Val substitution's impact on peptide restriction was significantly influenced by the presence of 71Arg versus 71Lys.
• Reducing peptide anchor residue bulk (149Trp to Phe) could overcome 86Val restriction, but this was harder with a concurrent 57Asp to Ser substitution.
• Combined 86Val and 57Ser substitutions had more drastic effects on peptide presentation than individual substitutions, even when peptide binding remained unchanged.

Conclusions:

• The configuration of the peptide-HLA-DR4 complex is critical for T cell recognition.
• Subtle conformational influences on the peptide or HLA-DRbeta alpha helix, arising from combined substitutions, significantly affect T cell recognition.
• The effects of individual HLA class II substitutions should be evaluated within their natural allelic context.