Expression of antigen recognized by 1B10 by a variety of cell types. Fibroblasts (A), human umbilical vein endothelial cells (HUVECs) (C), microvascular endothelial cells (MVECs) (D), and smooth muscle cells (E) were cultured and CD14⁺ monocytes (B), granulocytes (H), platelets (F), and red cells (RBCs) (G) were isolated as described in “Materials and methods.” These cells were then stained with 1B10 MoAb or a control murine monoclonal IgM, followed by rabbit antimouse IgM-FITC and analyzed by flow cytometry. Labeling with control IgM antibody is shown in solid filled curve. Open histograms denote cell-specific antibody.