The lymphocyte function-associated antigen 1 I domain is a transient binding module for intercellular adhesion...

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• The I domain of Lymphocyte Function-Associated Antigen-1 (LFA-1) possesses binding sites for Intercellular Adhesion Molecules (ICAM)-1 and ICAM-3.
• The precise role of this binding site in regulated cell adhesion remains unclear.

Purpose of the Study:

• To investigate the adhesive properties and functional characteristics of the LFA-1 I domain.
• To elucidate the mechanism by which the LFA-1 I domain contributes to cell adhesion dynamics.

Main Methods:

• Stable expression of a glycosylphosphatidylinositol-anchored LFA-1 I domain (I-GPI) on baby hamster kidney cells.
• Assessment of cell binding to soluble ICAM-1 (sICAM-1) and interactions on ICAM-1/ICAM-3 bilayers using flow cell experiments.
• Evaluation of the effects of the LFA-1 activating antibody MEM-83 and divalent cations (Mg2+, Mn2+) on cell adhesion.

Main Results:

• I-GPI cells exhibited low avidity and affinity binding to sICAM-1.
• Specific rolling interactions were observed between I-GPI cells and ICAM-1/ICAM-3 bilayers.
• The MEM-83 antibody reduced rolling velocity on ICAM-1 but blocked interaction with ICAM-3.
• Rolling was dependent on Mg2+, with Mn2+ partially substituting and increasing rolling velocity.

Conclusions:

• The LFA-1 I domain functions as a transient, Mg2+-dependent binding module.
• This module likely cooperates with a Mn2+-stimulated site within LFA-1 to mediate stable interactions with ICAM-1.
• These findings provide insights into the molecular mechanisms of LFA-1-mediated cell adhesion.