Immunocytochemical analyses of plasma cells from the patient with NSM and chemical characterization of the nonsecreted κ light chains. (A) Reactivity of bone marrow–derived plasma cells. The primary reagents included a murine antiplasma cell mAb and those specific for free or bound human κ light chains. Microscopic analyses were performed using a Leitz DMRB microscope (Vashaw Scientific, Norcross, GA) and objectives that included Leica HC PL Fluotar 40× and 10× lenses. The digital photographs were taken with a SPOT RT Model 2.2.0 camera (Diagnostic Instruments, Sterling Heights, MI) using SPOT RT software, version 3.0. Original magnification, × 400. (B) Coomassie blue-stained SDS/PAGE gel of protein contained in the plasma cell lysates (lane 1), molecular mass standards (lane 2), and a κ1 Bence Jones protein isolated from the urine of a patient with MM (lane 3). (C) Primary structure of the κ1 light chain isolated from plasma cell lysates. The N-terminal amino acid sequence was established directly and the remainder from tryptic peptides subjected to Edman degradation (ST) and mass spectrometry (MT). The residues in parentheses were deduced from cDNA cloned from the patient's plasma cells. The junction between the V_L and C_L domains is as designated and the anomalous residues after position 187 are italicized.