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CD8+ cytotoxic T lymphocyte activation by soluble major histocompatibility complex-peptide dimers

Marek Cebecauer1, Philippe Guillaume, Silke Mark

  • 1Ludwig Institute for Cancer Research, Lausanne Branch, University of Lausanne, 1066 Epalinges, Switzerland.

The Journal of Biological Chemistry
|April 5, 2005
PubMed

Insights

Cytotoxic T lymphocytes (CTLs) achieve high sensitivity by engaging two peptide-MHC (pMHC) complexes simultaneously. This dimeric binding mode enhances antigen recognition, crucial for immune responses.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cellular Biology

Background:

  • CD8+ cytotoxic T lymphocytes (CTLs) possess remarkable sensitivity, recognizing target cells with minimal peptide-MHC (pMHC) complexes.
  • The molecular mechanisms underlying this sensitive antigen recognition by CTLs remain incompletely understood.

Purpose of the Study:

  • To investigate the molecular basis of sensitive antigen recognition by CTLs.
  • To elucidate the binding mode of dimeric pMHC complexes with T cell receptors (TCRs).

Main Methods:

  • Studied dimeric pMHC complexes with varying linker lengths (10-30 Å vs. ≥80 Å).
  • Assessed binding affinity and T cell activation via calcium mobilization and phosphorylation assays.
  • Employed fluorescence resonance energy transfer (FRET) experiments to analyze binding interactions.

Main Results:

  • Dimeric pMHC complexes with short linkers efficiently bound to and activated cloned CTLs.
  • Dimeric pMHC complexes with long linkers failed to induce significant binding or activation.
  • A dimeric binding mode was identified where two TCRs engage two pMHC complexes anti-parallelly.

Conclusions:

  • This anti-parallel dimeric binding mode integrates low-affinity interactions, enhancing overall binding and CTL sensitivity.
  • The findings highlight the importance of pMHC complex presentation in modulating T cell-mediated immunity.
  • Activation of CTLs by pMHC dimers with one agonist and one null ligand supports this model.

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