Sjögren's syndrome (SS) is a unique disease which develops a high incidence of lymphoproliferative disorders (LPD) such as monoclonal gammopathy or malignant lymphoma. In order to elucidate the mechanism responsible for the emergence of monoclonal B cell proliferation at the site of a chronic autoimmune reaction, the rheumatoid factor (RF) related germline gene Vg and expression of the bcl-2 gene in the lymphoepithelial lesion (LEL) were studied. Predominant usage of the Vg or Vg-like genes was found in the peripheral blood leukocytes in SS patients and abundant expression of bcl-2 protein in the lymphocytes in and around the LEL were observed. These results suggest that RF clones were activated resulting into monoclonal proliferation and overexpression of bcl-2 protein play a role allowing the cell to escape a apoptotic cell death resulting into the increased risk of monoclonal proliferation in SS patients.