The interaction of Bordetella pertussis adenylate cyclase toxin (CyaA) with complement receptor 3 (CR3, CD11b/CD18) involves N-linked oligosaccharide chains. To investigate the relative importance of the individual N-glycans of CR3 for toxin activity, the asparagine residues of the consensus N-glycosylation sites of CR3 were substituted with glutamine residues that cannot be glycosylated. Examination of CR3 mutant variants and mass spectrometry analysis of the N-glycosylation pattern of CR3 revealed that N-glycans located in the C-terminal part of the CD11b subunit are involved in binding and cytotoxic activity of CyaA. We suggest that these N-glycans form a defined clustered saccharide patch that enables multivalent contact of CR3 with CyaA, enhancing both affinity and specificity of the integrin-toxin interaction.