(a) Case 1: interstitial edema (hematoxylin-eosin [H&E]) (left) and positive C4d staining (right); magnification,×400. (b) Case 2: H&E histology shows diffuse interstitial inflammation (left) and positive C4d staining (right); magnification, ×400. (c) Case 4: H&E from biopsy before bortezomib treatment showing minimal interstitial inflammation and myocytolysis (left) and positive C4d staining (right). Because the initial C4d stain showed diffuse staining of myocytes and the capillaries could not be recognized, the stain was repeated using a double stain with C4d (green, fluorescein isothiocyanate, capillaries) and actinin (red, Cy3, myocytes); magnification, ×400.