The alloreactive and self-restricted CD4+ T cell response directed against a single MHC class II/peptide combination

Area of Science:

• Immunology
• Transplant Rejection
• T cell Recognition

Background:

• Allograft rejection is driven by T cell responses to foreign Major Histocompatibility Complex (MHC) molecules.
• While MHC polymorphic residues were initially thought to be the primary target, MHC-bound peptides are critical for T cell recognition.
• The relative importance of MHC molecules versus bound peptides for alloreactive T cells remains debated.

Purpose of the Study:

• To investigate the role of MHC-bound peptides in alloreactive CD4+ T cell responses.
• To compare the reactivity of alloreactive T cells with self-restricted T cells against a specific MHC class II-peptide complex.
• To determine if alloreactive T cells are more dependent on MHC molecules than peptides.

Main Methods:

• Studied the response to the H2-Ab molecule bound with the Ep peptide.
• Generated alloreactive T cells specific for the Ab/Ep complex.
• Compared reactivity of alloreactive and self-restricted T cells to peptide stimulation and amino acid substitutions.

Main Results:

• The H2-Ab/Ep complex was a poor target and stimulator for alloreactive CD4+ T cells.
• Alloreactive T cells showed exquisite specificity for the Ab/Ep complex.
• Peptide-specific alloreactive T cells were more sensitive to peptide stimulation than self-restricted T cells.
• Alloreactive and self-restricted T cells exhibited equal sensitivity to peptide amino acid substitutions.

Conclusions:

• MHC-bound peptides are as important for alloreactive CD4+ T cells as they are for MHC class I-restricted cytotoxic T lymphocytes (CTL).
• Alloreactive and self-restricted T cells interact similarly with their MHC/peptide ligand.
• Findings contribute to understanding the molecular basis of transplant rejection and T cell recognition.