Characterization of molecular interactions between intercellular adhesion molecule-1 and leukocyte function-...

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Soluble ICAM-1 (sICAM-1) is known to inhibit ICAM-1/LFA-1 adhesion.
• Circulating ICAM-1 may modulate immune functions, necessitating a molecular understanding of its interaction with LFA-1.
• Previous studies reported sICAM-1 inhibition of in vitro assays across a wide concentration range.

Purpose of the Study:

• To determine the molecular affinity and avidity of the interaction between soluble ICAM-1 and LFA-1.
• To characterize the specificity of the ICAM-1/LFA-1 interaction using molecular assays.
• To assess the impact of ICAM-1 multimerization on binding affinity to LFA-1.

Main Methods:

• Direct binding experiments using biotinylated monomeric sICAM-1 and immobilized LFA-1.
• Competitive binding assays with unlabeled sICAM-1 and a truncated sICAM-1 variant (D1D2).
• Specificity characterization using monoclonal antibodies (mAbs) against sICAM-1 and LFA-1.
• Extension of assays to multimeric sICAM-1 using nonblocking mAbs against domains D4 and D5.

Main Results:

• Monomeric sICAM-1 exhibited a moderate binding affinity for immobilized LFA-1 (approximately 130 nM).
• Competitive binding experiments confirmed these affinities.
• Dimerization of sICAM-1 using specific mAbs increased the binding affinity for LFA-1 by two orders of magnitude (approximately 4 nM), attributed to avidity.
• Specificity was confirmed using anti-ICAM-1 and anti-LFA-1 mAbs.

Conclusions:

• The ICAM-1/LFA-1 interaction involves moderate affinity for monomers but high avidity for multimeric forms.
• Cell surface-expressed multimeric ICAM-1 likely binds cell surface-immobilized LFA-1 with very high avidity.
• Developed molecular assays are valuable for evaluating potential ICAM-1/LFA-1 antagonists.