Ultrastructural and immunoelectron microscopic studies on infiltrating mononuclear cells in lymphocytic...

The ultrastructural relations of the infiltrating mononuclear cells to the parenchymal tissues were studied in the submandibular gland of the female non-obese diabetic (NOD) mouse. In addition, the phenotype of mononuclear cells infiltrating the submandibular gland has been determined by light and electron microscopy by using monoclonal antibodies against T-cell subsets (Thy1.2, Lyt1, Lyt2). Ultrastructurally, lymphoid cells were frequently observed around and in the acini and ducts. Some of the lymphoid cells observed in the acini and ducts were irregular in shape and sometimes sent spike-like projections into acinar and ductal cells. Immunohistochemical study demonstrated that Thy1.2+ cells were predominant among the infiltrating cells, and the majority of these infiltrating T-cells were composed of Lyt1+ cells with a small proportion of Lyt2+ cells. By immunoelectron microscopy, lymphocytes carrying Thy1.2, Lyt1 or Lyt2 antigen were identified, as is demonstrated by an electron-dense reaction product on the entire cell surface, and these immunopositive cells were frequently observed around and in the acini and ducts. Some of the Thy1.2+, Lyt1+ or Lyt2+ cells observed in the acini and ducts demonstrated a close contact with acinar and ductal cells and both Lyt1+ and Lyt2+ cells sent spike-like projections into them. Occasionally, a partial degeneration of acinar cell adjacent to the invading lymphocytes was observed. These observations suggest that T-lymphocytes are involved in the direct destruction of acinar and ductal cells in the NOD mouse submandibular glands.