title: Abnormal expression of CD20 on IgG4 plasma cells associated with IgG4-related lymphadenopathy.
abstract: BACKGROUND
  Immunoglobulin G4 (IgG4)-related disease is a recently described entity that presents as mass-forming lesions in soft tissue, exocrine glands, and in lymph nodes as IgG4-related lymphadenopathy. The underlying pathologic mechanism of IgG4-related disease is unclear; however, rituximab (an anti-CD20 monoclonal antibody) has been shown to have clinical efficacy.
  
  
  OBJECTIVE
  To look for the presence or absence of CD20 on the IgG4-expressing plasma cells in IgG4-related lymphadenopathy.
  
  
  METHODS
  Twelve flow cytometry cases were identified through a retrospective review from the authors' institutions files. Cases were selected by the presence of a lymph node biopsy specimen with increased IgG4 plasma cells by immunohistochemistry and a histologic diagnosis compatible with IgG4-related lymphadenopathy.
  
  
  RESULTS
  We report dim CD20 expression on plasma cells in all cases for which a plasma cell population was clearly identified by flow cytometry. These cases were from patients with lymph node biopsy specimens that met published criteria for IgG4-related lymphadenopathy.
  
  
  CONCLUSIONS
  This finding may be one potential explanation for the clinical efficacy of rituximab in IgG4-related disease.
authors.affiliation: Department of Pathology, Clarient/GE Healthcare, Aliso Viejo, California 92656, USA. kgrimm@clarientinc.com
authors.forename: Kate E
authors.initials: KE
authors.lastname: Grimm
authors.forename: Antony
authors.initials: A
authors.lastname: Bakke
authors.forename: Dennis P
authors.initials: DP
authors.lastname: O'Malley
mesh_terms: D000328:Adult; D000368:Aged; D058846:Antibodies, Monoclonal, Murine-Derived / Q000276:immunology; D018951:Antigens, CD20 / Q000378:metabolism*; D001706:Biopsy; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D007150:Immunohistochemistry; D007155:Immunologic Factors / Q000276:immunology; D008206:Lymphatic Diseases / Q000276:immunology* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D010950:Plasma Cells / Q000276:immunology*; D012189:Retrospective Studies; D000069283:Rituximab
chemical_list: D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D007074:Immunoglobulin G; D007155:Immunologic Factors; D000069283:Rituximab