MONONUCLEAR-CELLS IN SALIVARY-GLANDS OF NORMAL AND ISOPROTERENOL-TREATED RATS

The purpose of this study was to analyse the phenotypical distribution of resident cells of the mononuclear phagocyte system in rat salivary glands, and to determine whether isoproterenol induces alterations in macrophage and lymphocyte surface-marker expression. Frozen sections of gland tissues were prepared from five normal rats, and from six rat s treated with 20 mg/kg isoproterenol/day for 10 days. A panel of six monoclonal antibodies was used to identify membrane markers associated primarily with monocytes (ED1), mature tissue macrophages (ED2), lymp hoid macrophages (ED3), MHC class II (Ia) antigens (OX6), CDS-positive T Iymphocytes (OX19), and rat B lymphocytes (OX33). Double-labelling techniques were used to detect the coexpression of ED1/ED2 and OX6/ED2 mononuclear cell markers in the major salivary glands. ED2 positive m acrophages were predominant in all three major glands, ranging from 96 cells/0.87 mm(2) field in the parotid gland to 165 cells/0.87 mm(2) i n the submandibular. OX19-positive T Iymphocytes were rarefy observed in submandibular and parotid glands but represented a distinguishing f eature of the sublingual. Moderate numbers of ED3-positive macrophages also were detected in sublingual tissues. In the submandibular and pa rotid glands, isoproterenol resulted in a decrease in ED2-positive cel ls, but ED2-positive macrophages increased in sublingual glands with i soproterenol. Isoproterenol resulted in a decrease in MHC class II ant igen expression on submandibular and sublingual mononuclear cells but an induction of Ia antigen in the parotid gland. Double labelling reve aled that isoproterenol induced coexpression of ED1/ED2 markers on mon onuclear cells in the submandibular glands, but ED1/ED2-positive cells were absent from other glands. However, coexpression of MHC class II markers on ED2-positive cells in the sublingual and parotid glands of normal rats was frequently observed, with isoproterenol decreasing coe xpression in the sublingual gland and increasing it in the parotid. B lymphocytes were not detected in any of the glands examined. These fin dings indicate that important differences exist in normal resident mon onuclear cell subsets among the major salivary glands of the rat. The differential effects of isoproterenol on inflammatory cells may reflec t important differences in local salivary gland immunoregulation. Alth ough salivary gland inflammation induced by isoproterenol does not app ear to result from immune mechanisms, the rich population of T lymphoc ytes and ED3-positive macrophages, and presence of MHC class II antige ns, suggest that the sublingual gland may function as an immune organ and have a role in mucosal immunity.