Blocking monoclonal antibodies to alpha V beta 3 integrin: a unique epitope of alpha V beta 3 integrin is present on human osteoclasts.

Integrins are a family of cell surface glycoproteins that promote cell adhesion. The integrin alpha V beta 3, vitronectin receptor, is a major integrin expressed by osteoclasts. To further investigate the role of alpha V beta 3 in cell adhesion, we generated and characterized monoclonal antibodies to alpha V beta 3 by immunizing BALB/c mice with purified alpha V beta 3 protein. Three monoclonal antibodies (mAbs), 9D4.9.1, 9G2.1.3, and 10C4.1.3, from a total of more than 1100 positive cultures which bound alpha V beta 3, were characterized extensively: mAbs 9G2.1.3 and 10C4.1.3 recognize the alpha V beta 3 complex whereas mAb 9D4.9.1 reacts with the beta 3-chain shared between the alpha V beta 3 complex and gpIIbIIIa. Further epitope mapping using flow microfluorometry analysis and histochemical staining of various tissues showed that 9D4.9.1 and 10C4.1.3 recognized distinct epitopes. Ligand-binding studies using cell-bound and purified alpha V beta 3 demonstrated that all three mAbs blocked fibrinogen binding. Vitronectin binding was blocked by mAb 9D4.9.1 and, less effectively, by mAb 10C4.1.3; mAb 9G2.1.3 was without effect. All three mAbs recognized osteoclasts from human tissues; mAb 9G2.1.3 also stained osteoclasts from a wide range of nonhuman species. Monoclonal antibodies 9D4.9.1 and 9G2.1.3 bound to a panel of cultured cell lines and various tissues. In contrast, mAb 10C4.1.3 bound only weakly or not at all to tissues expressing alpha V beta 3 with the exception of osteoclasts. Thus, mAb 10C4.1.3 showed a very narrow tissue specificity being restricted to high-level expression on human osteoclasts.