SLT-1 receptors are present on a B-cell subset of myeloma patients and absent on HPC. Cells from peripheral blood of myeloma patients (A and B) were stained with anti-CD19-PE and FITC-SLT-B. Mobilized blood mononuclear cells (C) were stained with anti-CD34-PE/anti-CD45-QR and FITC-SLT-B and files were gated for the HPC subset (D), as described in Materials and Methods. For (C) and (D), the arrows indicate the HPC subset. For myeloma, the peripheral blood includes both polyclonal and monoclonal B cells.24 The arrowhead indicates the monoclonal subset of B cells and the arrow highlights the polyclonal subset, presumptively normal B cells that lack SLT-1 receptors.