Nucleolar organizer regions (NORs) in lymphoproliferative disorders of the human salivary gland.

The relationship between the silver-stained proteins of the nucleolar organizer regions (AgNORs) and proliferative activity was studied in 30 patients with lymphoproliferative disorders of the major salivary gland. The salivary gland lesions were microscopically and immunohistochemically differentiated into myoepithelial sialadenitis (MESA, n = 6), low-grade B-cell lymphoma (n = 16), high-grade B-cell lymphoma (n = 5), and T-cell lymphoma (n = 3). The mean AgNOR count per nucleus for MESA was 2.48; for low-grade B-cell lymphoma, 2.19; for high-grade B-cell lymphoma, 6.37; and for T-cell lymphoma, 5.46. There was no significant difference in AgNOR counts per nucleus between the MESA and low-grade B-cell lymphoma, whereas the high-grade B-cell lymphomas exhibited significantly increased mean AgNOR number. Furthermore, the mean numbers of AgNOR were compared with cellular types of lymphoproliferative disorders. A statistically significant difference did exist among AgNOR counts of centroblasts, centrocytes and mantle zone lymphocytes or interfollicular lymphocytes in MESA. There was no significant difference in AgNOR counts per nucleus among the centroblasts of MESA, neoplastic centroblasts of centroblastic/centrocytic lymphoma, and centroblastic lymphoma. It was shown that AgNOR enumeration of tumor cells in mucosa-associated lymphoid tissue (MALT) lymphoma was similar to those seen in mantle zone and interfollicular lymphocytes of MESA. Therefore, we propose that MALT lymphoma may represent a mucosal counterpart of mantle zone lymphocyte- or interfollicular lymphocyte-related low-grade B-cell lymphomas.