FUNCTIONAL INTERACTION BETWEEN THE INTEGRIN ANTAGONIST NEUTROPHIL INHIBITORY FACTOR AND THE I-DOMAIN OF CD11B CD18/

Neutrophil inhibitory factor (NIF) is a hookworm-derived glycoprotein ligand of the integrin CD11b/ CD18 that inhibits human neutrophil func tion (Moyle, M., Foster, D. L., McGrath, D. E., Brown, S. M., Laroche, A., De Meutter, J., Stanssens, P., Bogowitz, C. A., Fried, V. A., Ely , J. A., Soule, H. R., and Vlasuk, G. P. (1994) J. Biol. Chem. 269, 10 008-10015). Here, we present evidence that recombinant NIF (rNIF) asso ciates with the similar to 200-amino acid residue I domain of CD11b/CD 18 and that this interaction is essential for inhibition of neutrophil function by NIF. First, radiolabeled rNIF binds to a recombinant glut athione S-transferase fusion protein that contains the CD11b I domain. This high affinity interaction has a partial dependence on divalent c ations. The association of rNIF with the CD11b I domain is specific be cause I-125-rNIF does not bind either a glutathione S-transferase fusi on protein that contains the I domain of the integrin CD11a/CD18 or re combinant glutathione S-transferase without the I domain. Second, the CD11b I domain fusion protein effectively competes with CD11b/ CD18 on human neutrophils for I-125-rNIF binding. Third, the CD11b I domain f usion protein blocks the inhibition of certain neutrophil functions by rNIF, including adhesion of neutrophils to human endothelial cell mon olayers and adhesion dependent release of hydrogen peroxide from neutr ophils. Specificity is demonstrated by the inability of the CD11a I do main fusion protein to block either rNIF binding to neutrophils or rNI F activity. Fourth, rNIF blocks the interaction between neutrophils an d fibrinogen, a CD11b/CD18 ligand that is also thought to bind the I d omain of CD11b. In contrast, rNIF does not appear to block the binding of factor X to CD11b/CD18 on neutrophils. These results suggest that CD11b/CD18 has multiple distinct binding sites for its cognate ligands , including, but not limited to, the I domain. NIF interferes with the binding of a subset of these CD11b/CD18 ligands in a highly selective manner.