AFFINITY AND KINETIC-ANALYSIS OF THE MOLECULAR INTERACTION OF ICAM-1 AND LEUKOCYTE FUNCTION-ASSOCIATED ANTIGEN-1

LFA-1 is a member of the beta(2) integrin family, and interacts with I CAM-1, a member of the Ig superfamily containing five Ig-like domains, interaction of LFA-I with ICAM-1 is important in a number of cellular events, including ag-specific T cell activation and leukocyte transen dothelial migration, which are known to he typically transient and hig hly regulated, in this study, we have used surface plasmon resonance t echnology to study the ICAM-1/LFA-1 interaction at the molecular level , A soluble form of LPA-1 (sLFA-1), normally expressed as two noncoval ently associated membrane-bound subunits, has been produced, and its i nteraction with ICAM-1 has beers examined. The kinetic analysis of a m onomeric sLFA-1 binding to the first two domains of ICAM-1 expressed a s a chimeric IgG fusion protein (DID2-IgG) revealed that sLFA-1 was ho und to the D1D2-IgG chimera with a K-d of 500 nM and dissociated with 11 k(diss) of 0.1 s(-1). Monomeric membrane-bound LFA-1 purified from plasma membranes showed a similar kinetic to sLFA-1, These results sug gest that the monovalent interaction between ICAM-P and LFA-1 has a pr imarily high affinity and a slow dissociation rate constant as compare d with other adhesion molecules, suggesting a potential mechanism for firm adhesion.