Renal transplant pathology: An update

Renal transplant pathology occupies an ever-changing spectrum, due to new techniques and drugs. Acute and chronic antibody-mediated rejection is diagnosed by a combination of light, immunofluorescence (C4d) and electron microscopic features, and these newly recognized diseases are now in the Banff schema. C4d deposition, with normal graft histology, is a sign of accommodation, most common in ABO-incompatible grafts. Chronic allograft nephropathy has been removed from the Banff system in an attempt to promote more specific diagnosis and treatment of the causes of late graft injury. A new aspect of polyomavirus is the formation of immune complexes along tubular basement membranes. Rapamycin causes lesions resembling myeloma cast nephropathy and exacerbates proteinuria, probably due to tubular and/or glomerular toxicity. Protocol biopsies, now part of routine care in many centers, detect the early stages of pathological processes, such as subclinical rejection, polyomavirus infection or transplant glomerulopathy, when they are potentially treatable.