RBT-3 induces prominent increases in HO-1 expression in mouse proximal tubules, as assessed by immunohistochemistry. The control kidney, shown in the left-hand panel, demonstrates variable cytoplasmic staining of proximal tubule segments within the renal cortex. In contrast, the kidney harvested 18 h post-RBT-3 injection (middle panel) showed a prominent and near-confluent proximal tubule HO-1 increase. In contrast, no obvious increase in HO-1 staining was apparent in the glomeruli (depicted by the asterisks) or medullary papillary regions (right-hand panel). Thus these findings confirmed that the HO-1 mRNA changes depicted in Figure 5 were reflected by increased renal HO-1 protein levels and that these increases reflected HO-1 increases predominantly within cortical proximal tubules.