MHC-peptide ligand interactions establish a functional threshold for antigen-specific T cell recognition

Area of Science:

• Immunology
• Molecular Biology

Background:

• T cell recognition relies on T cell receptor (TCR)-ligand interactions.
• The TCR-ligand complex involves specific MHC molecules and bound peptides.
• Understanding factors influencing T cell activation is crucial for immunology.

Purpose of the Study:

• To investigate how peptide affinity, concentration, and MHC density affect T cell proliferation.
• To determine the primary drivers of T cell activation in response to specific antigens.

Main Methods:

• Utilized a CD4+ T cell clone specific for HSV-2.
• Employed peptide analogs with varying DQ2-anchor residue mutations to alter peptide affinity.
• Adjusted MHC class II (DQ2) density on antigen-presenting cells (APCs) using B-LCLs.

Main Results:

• T cell proliferation decreased in a peptide-affinity and concentration-dependent manner.
• Weaker binding peptides resulted in reduced T cell responses.
• Varying MHC class II density on APCs did not significantly affect T cell proliferation.

Conclusions:

• Peptide-MHC avidity is the dominant factor in T cell clone activation.
• The T cell clone exhibits a low activation threshold.
• Ligand signal strength is primarily determined by peptide-MHC binding characteristics.