title: Immunophenotyping of interstitial infiltrate does not distinguish between BK virus nephropathy and acute cellular rejection.
abstract: BACKGROUND
  BK virus nephropathy (BKVN) is a significant cause of late renal allograft loss. It is characterized histologically by an interstitial nephritis that can be difficult to distinguish from acute cellular rejection (ACR). We investigated whether immunophenotyping of the infiltrate would aid this distinction.
  
  
  METHODS
  Ten cases of biopsy-proven BKVN, following renal transplantation, were identified from a single transplant centre. The infection was confirmed by renal biopsy and staining for SV-40 T-antigen. Biopsies from 20 consecutive patients with ACR were identified and used as controls. There was no evidence of BK infection serologically or histologically in these patients. Immunohistochemical staining with anti-CD20, perforin and granzyme B was performed on remaining tissue samples.
  
  
  RESULTS
  Clustered B cells were demonstrated in both BKVN and ACR. Hence, the CD20-stained component within the interstitial infiltrate was not useful in distinguishing these biopsies. Perforin-stained slides demonstrated fewer cytotoxic T cells in the biopsies with BK virus (average 2.4 +/- 1.4 cells per 100 lymphocytes per field) compared with those samples with acute rejection (8.6 +/- 5.7 cells per 100 lymphocytes, P < 0.0001). No significant difference in granzyme B staining was detected between ACR and BKVN.
  
  
  CONCLUSIONS
  Clustered B cells and granzyme B staining did not differentiate between ACR and BKVN. However, ACR cellular infiltrate was rich in perforin positive cells suggesting that perforin staining may be a useful marker to discriminate between these conditions.
authors.affiliation: Department of Nephrology and Transplantation Services, Basil Hetzel Institute, The Queen Elizabeth Hospital, Woodville, South Australia, Australia.
authors.forename: Natasha M
authors.initials: NM
authors.lastname: Rogers
authors.forename: Graeme R
authors.initials: GR
authors.lastname: Russ
authors.forename: John
authors.initials: J
authors.lastname: Cooper
authors.forename: P Toby
authors.initials: PT
authors.lastname: Coates
mesh_terms: D000208:Acute Disease; D000328:Adult; D001739:BK Virus; D005260:Female; D006084:Graft Rejection / Q000276:immunology*; D006801:Humans; D007150:Immunohistochemistry; D016130:Immunophenotyping; D007674:Kidney Diseases / Q000276:immunology* / Q000473:pathology; D016030:Kidney Transplantation / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D054353:Perforin / Q000032:analysis; D027601:Polyomavirus Infections / Q000276:immunology*; D014184:Transplantation, Homologous; D014412:Tumor Virus Infections / Q000276:immunology*
chemical_list: D054353:Perforin