Fig. 6. Examples of the Banff polyomavirus histologic classes. Class 1: (A) Simian virus 40 (SV40) staining (arrows) in <1% of the tubules (polyomavirus load [pvl] 1; ×200). (B) There is minimal interstitial fibrosis (ci0) (Jones methenamine silver, ×100). Class 2: (C) There are 1%–10% tubules with cells staining for SV40 (pvl 2), although one tubule has many infected cells (arrow; ×400). (D) There is mild interstitial fibrosis (ci1) with inflammation (arrows; PAS, ×100). Class 2: (E) >10% of the tubules have infected epithelial cells (arrows; pvl 3; ×200). (F) Minor interstitial fibrosis (ci0; PAS, ×100). Class 3: (G) There is extensive (>10%) tubular infection with BK virus (pvl 3) shown by SV40 staining (×40). (H) Severe (>50%) interstitial fibrosis with inflammation (ci3; arrows; PAS, ×40).
