Table 2 Banff classification of inflammatory cells in peritubular capillaries (PTCs), degree of interstitial fibrosis (IF/TA), and stages of polyomavirus infection (BKN)
PTC 0 | No significant cortical peritubular inflammatory changes |
PTC 1 | Cortical peritubular capillary with 3–4 luminal inflammatory cells |
PTC 2 | Cortical peritubular capillary with 5–10 luminal inflammatory cells |
PTC 3 | Cortical peritubular capillary with >10 luminal inflammatory cells |
IF/TA 0 | No interstitial fibrosis and tubular atrophy |
IF/TA 1 | Mild interstitial fibrosis and tubular atrophy (<25% of cortical area) |
IF/TA 2 | Moderate interstitial fibrosis and tubular atrophy (26–50% of cortical area) |
IF/TA 3 | Severe interstitial fibrosis and tubular atrophy/ loss (>50% of cortical area) |
BKN- stage A | Viral activation in cortex and/or medulla with intranuclear inclusion bodies AND/OR positive immunohistochemistry or in situ hybridization signals, no or minimal tubular epithelial cell necrosis/lysis, no denudation of tubular basement membranes, no or minimal interstitial inflammation in foci with viral activation, no or minimal tubular atrophy and interstitial fibrosis |
BKN- stage B | Marked viral activation in cortex and/or medulla, marked virally induced tubular epithelial cell necrosis/lysis and associated denudation of tubular basement membranes, interstitial inflammation, interstitial fibrosis and tubular atrophy |