VLA-β1 Integrin Subunit-Specific Monoclonal Antibodies MB1.1 and MB1.2: Binding to Epitopes Not Dependent on Thymocyte Development or Regulated by Phorbol Ester and Divalent Cations
We report here the isolation of two new monoclonal antibodies (MB1.1 and MB1.2) against mouse VLA-β1 integrin subunit. Characterization by flow cytometry demonstrated binding of MB1.1 and MB1.2 to freshly isolated thymocytes, primary bone marrow mast cell lines, as well as cell lines of distinct lineage each expressing different combination of VLA integrins. The specificity of MB1.1 and MB1.2 was determined by (1) their binding to antigen with Mr about 120 kDa, and (2) the ability of antiserum against the carboxyl terminal of VLA-β1 subunit to deplete antigens for MB1.1 and MB1.2 in sequential immunoprecipitation experiments. The epitopes for MB1.1 and MB1.2 were in close proximity to each other since preincubation of cells with one MAb inhibited the binding of the other. However, MB1.1 and MB1.2 differed in their affinity for the β1 subunit. In addition, neither MAbs had any effect on cell adhesion to matrix proteins indicating that the epitopes involved are distant from VLA integrin ligand-binding sites...