Force spectroscopy of LFA-1 and its ligands, ICAM-1 and ICAM-2

Area of Science:

• Biophysics
• Cellular Immunology
• Molecular Interactions

Background:

• Leukocyte function-associated antigen-1 (LFA-1) is a crucial T cell receptor mediating immune cell adhesion.
• Intercellular adhesion molecules (ICAM-1 and ICAM-2) are key ligands for LFA-1, playing roles in immune cell trafficking and activation.
• Understanding the mechanical properties of LFA-1/ICAM interactions is vital for comprehending immune synapse formation and function.

Purpose of the Study:

• To characterize the single-molecule force dynamics of LFA-1 interactions with ICAM-1 and ICAM-2 using atomic force microscopy (AFM).
• To investigate the influence of loading rate and magnesium ions on the binding strength and dissociation mechanisms of these adhesion complexes.
• To elucidate the differences in dynamic strength between LFA-1/ICAM-1 and LFA-1/ICAM-2 interactions.

Main Methods:

• Single-molecule force spectroscopy was performed using atomic force microscopy (AFM) to measure unbinding forces.
• LFA-1 expressed on Jurkat T cells was used to probe interactions with immobilized ICAM-1 and ICAM-2.
• Force spectra were acquired across a wide range of loading rates (50-60,000 pN/s) to analyze dynamic force behaviors.
• The effect of Mg(2+) on LFA-1 binding was assessed in the slow loading regime.

Main Results:

• Both LFA-1/ICAM-1 and LFA-1/ICAM-2 interactions exhibited distinct fast and slow loading regimes, indicating complex dissociation mechanisms involving inner and outer activation barriers.
• The binding strength of LFA-1 to both ICAM-1 and ICAM-2 was enhanced by Mg(2+) in the slow loading regime.
• The LFA-1/ICAM-2 complex displayed greater responsiveness to pulling forces compared to LFA-1/ICAM-1, attributed to wider activation barriers.

Conclusions:

• The dissociation of LFA-1/ICAM complexes involves overcoming energy barriers, with distinct characteristics for each interaction.
• Magnesium ions play a significant role in strengthening LFA-1 adhesion, particularly under slower force application.
• Differences in the mechanical properties of ICAM-1 and ICAM-2 influence the dynamic strength and force sensitivity of LFA-1-mediated cell adhesion.