CAM5.2-positive subserosal myofibroblasts in appendicitis.

In this study, we examined the distribution and origin of myofibroblasts around the perforations of appendicitis. Stromal cells of 45 cases were studied by immunohistochemistry. In the normal appendix, myofibroblasts were restricted to the mucosa, and CD34-positive stromal cells were distributed in the submucosal and subserosal layers. Some mesothelial cells were positive for cytokeratin CAM5.2, cytokeratin 5, or mesothelial cells (HBME-1). In perforation of appendicitis with both abscess and granulation tissue, a small to moderate or a moderate to large number of myofibroblasts appeared in the subserosal area around the perforation, respectively, but CD34-positive stromal cells were completely absent there. In the subserosal area of the perforation of appendicitis with abscess, cytokeratin 5-positive stromal cells were absent. However, a small to moderate number of cytokeratin CAM5.2-positive stromal cells were observed there. Double immunostaining showed the coexpression of alpha-smooth muscle actin (ASMA) and cytokeratin CAM5.2 and the coexpression of cytokeratin 5 and cytokeratin CAM5.2 in many or some stellate-shaped or spindle-shaped stromal cells existing in the subserosal area with granulation tissue around the perforation of appendicitis, respectively. Finally, many myofibroblasts appearing in the subserosal area of the perforation of appendicitis may be derived from submesothelial cells or mesothelial cells.