title: Inability of a monoclonal anti-light chain antibody to detect clonal plasma cells in a patient with multiple myeloma by multicolor flow cytometry.
abstract: BACKGROUND
  Multicolor flow cytometry (MFC) is increasingly important for the diagnosis and minimal residual disease (MRD) assessment of patients with plasma cells (PC) dyscrasias, like multiple myeloma. Recently published information shows that immunophenotype of myeloma PC can change over time and normal PC are heterogeneous in the expression of CD19 and CD56. This implies that for a sensitive, reliable detection of MRD clonality assessment by the detection of cytoplasmic kappa and lambda light chains is advisable.
  
  
  METHODS
  Eight-color MFC was used to detect normal and myeloma PC by the expression of CD38 and CD138. Analysis of additional surface antigens like CD45, CD19, CD56, CD27, and the intracellular immunoglobulin light chain distribution were used to differentiate polyclonal from clonal PC.
  
  
  RESULTS
  Absence of cytoplasmic light chains expression in a PC subpopulation with an abnormal phenotype suggested the presence of non-secretory plasma cells in the bone marrow (BM) of this patient. This observation however, was contradicted by the presence of free lambda light chains in the patient's serum. After repeating the analysis with polyclonal antibodies against intracellular immunoglobulin light chains instead of monoclonal antibodies, the abnormal PC subpopulation appeared to express lambda light chains.
  
  
  CONCLUSIONS
  These data illustrate that if clonality assessment of PC is included in disease monitoring, the use of polyclonal over monoclonal antibodies is preferred for the detection of intracellular immunoglobulin light chains.
authors.affiliation: Department of Medical Immunology, University Medical Centre Utrecht, Utrecht, The Netherlands. J.vanvelzen@umcutrecht.nl
authors.forename: Jeroen F
authors.initials: JF
authors.lastname: van Velzen
authors.forename: Dorine
authors.initials: D
authors.lastname: van den Blink
authors.forename: Andries C
authors.initials: AC
authors.lastname: Bloem
mesh_terms: D051997:ADP-ribosyl Cyclase 1 / Q000032:analysis; D000911:Antibodies, Monoclonal / Q000276:immunology*; D018941:Antigens, CD19 / Q000032:analysis; D019002:CD56 Antigen / Q000032:analysis; D005434:Flow Cytometry; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000276:immunology*; D017493:Leukocyte Common Antigens / Q000032:analysis; D009101:Multiple Myeloma / Q000175:diagnosis*; D010950:Plasma Cells / Q000276:immunology*; D053668:Syndecan-1 / Q000032:analysis; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7 / Q000032:analysis
chemical_list: D000911:Antibodies, Monoclonal; D018941:Antigens, CD19; D019002:CD56 Antigen; D007147:Immunoglobulin Light Chains; D053668:Syndecan-1; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7; D017493:Leukocyte Common Antigens; D051997:ADP-ribosyl Cyclase 1