DIFFERENCES IN THE BINDING OF BLOCKING ANTI-CD11B MONOCLONAL-ANTIBODIES TO THE A-DOMAIN OF CD11B

CD11b/CD18 (Mac-1) is a leukocyte integrin that plays a critical role in neutrophil adhesion and the initiation of acute inflammatory responses. Several Mac-1 blocking mAbs bind to the A-domain of CD11b, a similar to 200 amino acid region in the N-terminal portion of the protein that is involved in ligand binding and Mac-1 functional activity. We examined several CD11b blocking mAbs for different patterns of binding to the A-domain. We used human/murine chimeric CD11b expression constructs and deletions of the A-domain to examine binding. We describe the binding characteristics of mAbs 60.1, LM2/1, LPM19C, M170, 44, and 904. All of these mAbs, except for 60.1, bind to the C-terminal half of the human A-domain (CD11b(181-316)). mAb 60.1 was unique in that it required regions of the N- and C-terminal ends of the A-domain for binding. mAbs 60.1, LPM19C, 904, and 44 all required the A-domain to be intact for binding. This suggests that these CD11b mAbs recognize a conformational epitope. LM2/1 was capable of binding to a fragment of the A-domain, CD11b(285-300). Inasmuch as this system has been used to define different mAb binding sites, it may be used to analyze specific ligand binding sites in the A-domain of CD11b.