Figure 1. Histopathology of hyperacute rejection in human renal allografts: microscopic view (original magnification ×160) of a glomerulus in a biopsy taken from a human renal allograft that experienced hyperacute rejection. Tissue sections of the fixed biopsy specimen were stained with haematoxylin and eosin to reveal morphology. Note that most of the capillaries in the glomerulus are occluded with light pink thrombus (T). Some darker staining red blood cells are also present. In addition, polymorphonuclear leucocytes (P) can be found within the glomerular tissues. In normal kidneys, the capillaries of the glomerulus have clear nonoccluded lumens, and no polymorphonuclear neutrophils are present.

Figure 2. Histopathology of acute rejection in human renal allografts: microscopic view (original magnification ×160) of renal tubules in a biopsy taken from a human renal allograft that experienced acute rejection. Tissue sections of the fixed biopsy specimen were stained with periodic acid–Schiff to reveal morphology. Note that the tubules (T), each of which is surrounded by a red band of basement matrix, are widely separated by large numbers of infiltrating leucocytes (infiltrated regions indicated by stars), each containing a dark blue nucleus. The small white arrows identify leucocytes that have invaded the renal tubule, resulting in the tubulitis that is diagnostic for acute renal allograft rejection. In normal kidneys, there is no leucocytic infiltration and the renal tubules are juxtaposed to one another.

Figure 3. Histopathology of chronic rejection in human renal allografts: microscopic view (original magnification ×80) of a large artery in a biopsy taken from a human renal allograft that experienced chronic rejection. Tissue sections of the fixed biopsy specimen were stained with haematoxylin and eosin to reveal morphology. Note that the central lumen (L) is quite small. At the time of transplantation, the lumen occupied a space that began just inside the internal elastic lamina (E). The material that now occupies this space (the tissue between paired, opposing, black arrows) is neointima (N). This neointima, which is a diagnostic feature of chronic rejection, is composed of several cell types (blue nuclei) imbedded in large amounts of extracellular matrix.