Distribution of factor XIIIa-containing cells and collagenous components in radicular cysts: histochemic and immunohistochemic studies.

The distribution of subunit A of Factor XIII (FXIIIa) and of collagenous components was investigated by the avidin-biotin-peroxidase complex (ABC) method for FXIIIa and by the Sirius red F3BA method, respectively, in 43 cases of radicular cysts. Besides the covering epithelial layer, the radicular cyst wall was composed of the following three layers: an inner granulomatous layer, an outer fibrous connective tissue layer, and an intermediate layer. In each layer, a positive reaction for FXIIIa was observed in certain connective tissue cells. These FXIIIa-containing cells were few in number in the inner layer where collagenous components were also sparse. In the slightly to moderately fibrous intermediate layer, these cells markedly increased in number and were dendritic or stellate in shape. In the outer densely fibrous connective tissue layer, they decreased slightly in number and were slender and spindle-shaped. The results obtained in the present study indicate the close relationship between the distribution of FXIIIa-containing cells and of collagenous components. Such a relationship suggests that these cells play an important role in the process of fibrosis occurring in the radicular cyst wall.