Histopathogenesis of spontaneous periodontal disease in conventional rats: III. The mononuclear cell infiltrate and cytoplasmic changes in associated fibroblasts

Spontaneously developing periodontitis lesions in rats fed a regular pelleted chow and a powdered high sucrose diet were examined by electron microscopy. Inflamed connective tissue contained numerous monocytes and large and small lymphocytes. Most large lymphocytes possessed the cytoplasmic features of blast‐type cells. Fibroblasts located within the inflamed connective tissue were found to be closely juxtaposed to mononuclear cells, many clearly belonging to the lymphocyte line. A narrow intercellular space separated adjacent cells in these fibroblast‐lymphocyte aggregates. Although the fibroblasts did not demonstrate the characteristic features usually attributed to cytotoxic damage, they did contain an increased number of dense and pleomorphic granules which contained poorly polymerized collagenous material. These features resemble, in part, those seen in colchicinetreated fibroblast suggesting that collagen secretion may be impaired in fibroblasts closely juxtaposed to lymphocytes in inflamed periodontal connective tissue.