Figure 8. Banff Lesion Score C4d. A, IHC staining with peroxidase yielding a brown reaction product for C4d. An example of C4d3, this image demonstrates linear and circumferential staining of endothelial cells in virtually all peritubular capillaries. The staining was similar in all areas of the cortex and the medulla. The proportion of stained peritubular capillaries and medullary vasa recta informs the score. Immunoperoxidase, original magnification x400 B, IF staining for C4d. This image shows an example of a Banff Lesion Score of C4d3; using IF, a minimum score of C4d ≥ 2 is considered positive. In addition to this, the staining intensity for an individual capillary or medullary vas rectum must be at least 1+ on the usual scale from negative, trace, 1+, 2+ to 3+. Indirect IF, mouse antihuman C4d followed by fluorescein isothiocyanate-conjugated anti-mouse IgG, original magnification x100.