title: Dense IgG4 plasma cell infiltrates associated with chronic infectious aortitis: implications for the diagnosis of IgG4-related disease.
abstract: BACKGROUND
  IgG4-related aortitis is a newly recognized form of noninfectious aortitis that occurs as part of the spectrum of a systemic disease referred to as IgG4-related disease. IgG4-related aortitis is distinguished from giant cell aortitis and Takayasu aortitis in part by the presence of increased numbers of IgG4-expressing plasma cells. Chronic infectious aortitis can also display lymphoplasmacytic infiltrates, but the degree of IgG4 expression in these cases has not been specifically evaluated.
  
  
  METHODS
  Two cases of chronic active infectious abdominal aortitis were prospectively identified. Both were due to gram-positive bacteria, and at least one of the cases was due to chronic active Staphylococcus aureus infection. The degree of IgG4 plasma cell infiltration was assessed by immunohistochemistry.
  
  
  RESULTS
  Both cases of chronic infectious aortitis focally displayed high levels of IgG4-expressing plasma cells, greater than 50% of the IgG-expressing plasma cells, and greater than 50 IgG4-expressing plasma cells per high-power field.
  
  
  CONCLUSIONS
  Focal dense IgG4 plasma cell infiltrates can be seen in association with chronic infectious aortitis due to gram-positive bacteria, including Staphylococcus aureus. This observation supports the proposal that chronic Staphylococcus aureus infection may stimulate a Th2-mediated elevation in IgG4. The pathologic diagnosis of IgG4-related aortitis should not be based solely on the presence of increased IgG4 plasma cell counts from immunohistochemistry, but requires consideration of the overall pathology, including careful exclusion of infectious aortitis.
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston MA, 02114, USA.
authors.forename: Zakir
authors.initials: Z
authors.lastname: Siddiquee
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Zane
authors.forename: R Neal
authors.initials: RN
authors.lastname: Smith
authors.forename: James R
authors.initials: JR
authors.lastname: Stone
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001012:Aorta, Abdominal / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D001025:Aortitis / Q000175:diagnosis* / Q000276:immunology / Q000382:microbiology; D001424:Bacterial Infections / Q000175:diagnosis* / Q000276:immunology; D002908:Chronic Disease; D017809:Fatal Outcome; D005260:Female; D006094:Gram-Positive Bacteria / Q000302:isolation & purification; D006801:Humans; D007154:Immune System Diseases / Q000175:diagnosis* / Q000276:immunology / Q000382:microbiology; D007074:Immunoglobulin G / Q000378:metabolism*; D018655:Lymphocyte Count; D008297:Male; D010950:Plasma Cells / Q000276:immunology / Q000473:pathology*; D011446:Prospective Studies
chemical_list: D007074:Immunoglobulin G