High molecular weight kininogen binds to Mac-1 on neutrophils by its heavy chain (domain 3) and its light chain (domain 5).

High molecular weight kininogen (HK) binds specifically, saturably, and reversibly to neutrophils and also reciprocally inhibits the binding of fibrinogen to neutrophils. Since fibrinogen binds to the leukocyte integrin CD11b/18 (Mac-1, alpha M beta 2), we investigated whether HK bound to Mac-1 and whether the binding site was similar to that for factor X. We also examined whether one or both chains of cleaved HK (HKa) were involved. Two monoclonal antibodies, 2B5 (0.29 microM) to HK heavy chain domains 2 (D2) and 3 (D3), and C11C1 (0.26 microM) to HK light chain domain 5 (D5), inhibited by 99 and 93% the binding, respectively, of 125I-HK (8.3 nM) to neutrophils. To minimize steric hindrance, we further demonstrated that the Fab' fragments of 2B5 and C11C1 were able to inhibit the binding of this ligand to virtually the same extent as the intact antibody, indicating that, as in binding of HK to platelets and endothelial cells, both chains are involved. To directly demonstrate the involvement of each chain, we showed that the reduced alkylated light chain derived from HK and low molecular weight kininogen, which contains the same heavy chain as HK, each markedly inhibited the binding of HK to neutrophils. We localized the domain responsible for the binding in each chain by showing that recombinant D3 and D5 decreased the binding of HK to neutrophils. To define the receptor for HK, we employed three monoclonal antibodies to Mac-1: OKM1 and OKM10 to epitopes on the alpha M subunit and IB4 to an epitope on the beta 2 chain. OKM1, which can inhibit fibrinogen binding to neutrophils, inhibited HK binding by 79%, whereas the other antibodies inhibited HK binding less than 25%. Coagulation factor X also binds to Mac-1 on monocytes at a similar site to C3bi. Synthetic peptides which define noncontiguous surface loops in factor X that interact with Mac-1, failed to inhibit 125I-HK binding to neutrophils. We conclude that HK binds, via domains on its heavy chain, D3, and light chain, D5, to Mac-1 on the neutrophil surface, and HK occupies a site overlapping with fibrinogen and different from factor X.