Generation and characterization of an anti-idiotypic antibody specific for intercellular adhesion molecule-1

Intercellular adhesion molecule-1 (ICAM-1) is an inducible ligand for the LFA-1/MAC-1 family of leukocyte adhesion molecules. The results reported herein show that a mouse monoclonal anti-idiotypic antibody, CA3, specific for R6.5 anti-ICAM-1 mAb, shares conformational homology with the original epitope bound by R6.5. The CA3 bound specifically to R6.5 F(ab) fragments and blocked the binding of R6.5 to its ICAM-1 epitope; no CA3 binding was detected to a second anti-ICAM-1 mAb F(ab) fragment nor to control mouse IgG F(ab) fragments. Similarly, the interaction of CA3 with R6.5 was inhibited by sICAM-1. However, CA3 was ineffective in inhibiting CD18-dependent cell aggregation. A rabbit anti-CA3 response (Ab3) further indicated that CA3 is of the Ab2 beta type. Significant binding of anti-CA3 to sICAM-1 was demonstrated and anti-CA3 competed with R6.5 for binding to sICAM-1. Anti-CA3 bound to both soluble and cell-surface-associated ICAM-1. However, unlike R6.5, significant binding both to reduced sICAM-1 and to native sICAM-1 was exhibited by anti-CA3, whereas the binding of R6.5 to reduced sICAM-1 was undetectable.