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Integrins on rat osteoclasts: Characterization of two monoclonal antibodies (F4 and F11) to rat β3

Two monoclonal antibodies, F4 and F11, were raised to newborn rat bone cell suspensions. These antibodies are shown by immunocytochemistry on tissue sections to recognize an antigen shared between osteoclasts, megakaryocytes, and platelets. Immunoprecipitation analysis of the antigen from C6 rat glial cells followed by SDS‐PAGE showed a heterodimeric molecule with a characteristic integrin‐like shift in apparent molecular mass upon reduction (137/78 kD nonreduced; 118/100 kD reduced); the low‐molecular‐mass band comigrates with the β3 subunit precipitated with polyclonal antihuman vitronectin receptor antiserum, and the high‐molecular‐mass band comigrates with the αv subunit precipitated with a polyclonal antiserum to a C‐terminal amino acid sequence of human αv. Antibody F4 strongly cross‐reacts with human cells and is shown in cross‐blocking experiments and immunoprecipitation analysis with a human melanoma cell line DX3 to recognize a seemingly identical molecule as identified by anti‐αvβ3 monoclonal antibody 23C6. Expression of F4 and F11 is reduced in platelets from a patient heterozygous for Glanzmann's thrombasthenia. Taken together, these results indicate that F4 and F11 recognize rat CD61, the integrin β3 chain, which, as was confirmed with polyclonal anti CD61 antisera, is highly expressed in rat osteoclasts. These antibodies may be useful tools in investigating the biochemical nature and biologic function of β3 integrins in rat osteoclasts. Additionally, because high expression of β3 in vivo is restricted to osteoclasts, megakaryocytes, and platelets, these antibodies may be used to help identify osteoclasts in tissue sections and bone cell suspensions. Apart from β3, rat osteoclasts were found to express high levels of αv and β1 integrins.