Lymphoid tissue in rat oral mucosa: structure and function

Lymphocyte and macrophage/dendritic cell populations in the oral cavity of the rat were studied by immunohistochemistry. Furthermore, the reactivity of the oral mucosa towards antigen and its position in the mucosal immune system was investigated by staining antibody-forming cells and comparing serum and saliva antibody titres. Although numerous lymphocytes and non-lymphoid cells were present in the oral mucosa, organized lymphoid tissue could not be found. The majority of the lymphocytes are T cells, particularly of the T-helper phenotype. Macrophages were found only in the connective tissue, whereas dendritic cells also occurred in the epithelium. The possible functions of the cells in the different sites of the oral mucosa are discussed. Antibody-forming cells were mainly detected in the draining superficial and posterior cervical lymph nodes and in the submandibular glands. The roles of the various compartments of the oral mucosal immune system are discussed with particular reference to the epithelium and connective tissue as induction sites, the draining lymph nodes as sites of proliferation and differentiation, and the submandibular glands as effector sites.