Inflammation occurs when the body's defense system recognizes a foreign object (such as a transplanted kidney), and responds by sending white blood cells to attack the foreign object. These cells and the substances they produce can damage the transplanted kidney. There is currently no standard treatment for inflammation in the kidney; some transplant centers do not treat inflammation at all. Rejection is a more severe form of inflammation and injury. Both inflammation and rejection are diagnosed by looking at a piece of kidney (a kidney biopsy) under a microscope. Kidneys that have inflammation and/or rejection do not work as well or last as long as kidneys without injury.