Figure 103

Tubulitis is not absolutely specific for acute rejection. It can be found in mild forms in acute tubular necrosis, normally functioning kidneys, and in cyclosporine toxicity and in conditions not related to rejection. Therefore, quantitation is necessary. The number of lymphocytes situated between and beneath tubular epithelial cells is compared with the number of tubular cells to determine the severity of tubulitis. Four lymphocytes per most inflamed tubule cross section or per ten tubular cells is required to reach the threshold for diagnosing rejection. In this figure, the two tubule cross sections in the center have eight mononuclear cells each. Rejection with intimal arteritis or transmural arteritis can occur without any tubulitis whatsoever, although usually in well-established rejection both tubulitis and intimal arteritis are observed.

FIGURE 10-4 (see Color Plate)

In this figure the tubules with lymphocytic invasion are atrophic with thickened tubular basement membranes. There are 13 or 14 lymphocytes per tubular cross section. This is an example of how a properly performed periodic acid-Schiff (PAS) stain should look. The Banff classification is critically dependent on proper performance of PAS staining. The invading lymphocytes are readily apparent and countable in the tubules. In the Banff 1997 classification one avoids counting lymphocytes in atrophic tubules, as tubulitis there is more "nonspecific" than in nonatrophed tubules. (From Solez et al. [1]; with permission.)

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