title: C4d immunohistochemical stain is a sensitive method to confirm immunoreactant deposition in formalin-fixed paraffin-embedded tissue in bullous pemphigoid.
abstract: BACKGROUND
  Bullous pemphigoid (BP) is characterized clinically by the onset of pruritic urticarial plaques, vesicles and bullae in a predominantly elderly population. While the diagnosis may be suspected on routine hematoxylin and eosin histology of formalin-fixed paraffin-embedded tissue, fresh-frozen tissue must be used to show the immunologic nature of the bullous process by direct immunofluorescence (DIF). The diagnosis is further confirmed and separated from epidermolysis bullosa acquisita (EBA) by subsequent serologic studies to detect antibodies directed against BP180 and BP230 antigens and characteristic antibody deposition on salt-split skin.
  
  
  METHODS
  Using a polyclonal complement fragment 4d (C4d) antibody, we stained formalin-fixed paraffin-embedded skin biopsy specimens from cases of BP and controls.
  
  
  RESULTS
  We showed characteristic linear basement membrane deposition of C4d in formalin-fixed paraffin-embedded tissue in seven of nine cases diagnosed as BP vs. EBA by DIF on fresh-frozen tissue. None of the four controls for which we had adequate tissue were positive.
  
  
  CONCLUSIONS
  These results indicate that formalin-fixed paraffin-embedded tissue can be stained for the immunoreactant C4d to show characteristic immunoreactant deposition, potentially obviating the need for repeat biopsy for DIF and allowing clinicians to proceed to serologic confirmation of BP.
authors.affiliation: Department of Pathology, University of Utah, Salt Lake City, UT, USA. wells.chandler@hsc.utah.edu
authors.forename: Wells
authors.initials: W
authors.lastname: Chandler
authors.forename: John
authors.initials: J
authors.lastname: Zone
authors.forename: Scott
authors.initials: S
authors.lastname: Florell
mesh_terms: D001485:Basement Membrane / Q000378:metabolism; D015935:Complement C4b / Q000378:metabolism*; D005557:Formaldehyde; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods*; D016612:Paraffin Embedding; D010391:Pemphigoid, Bullous / Q000175:diagnosis* / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism*; D012680:Sensitivity and Specificity; D013194:Staining and Labeling / Q000379:methods*; D016707:Tissue Fixation
chemical_list: D010446:Peptide Fragments; D005557:Formaldehyde; D015935:Complement C4b; C032261:complement C4d