Abstract
The origin of cells comprising the capsule which forms around free-floating intraperitoneal blood clots has been examined in rats. One day after implantation the surface of the clot was covered by 1–2 layers of rounded nucleated cells. The majority of these cells were monocyte/macrophage in type with many cytoplasmic folds. Over the next 2 wk a thick capsule composed of dense connective tissue and myofibroblasts developed, completely covering the clot. The surface became covered by a contiguous layer of mesothelial cells, apparently derived from displaced cells of the damaged peritoneum. Detailed examination of the formation of the capsule suggested that a proportion of cells with the characteristic features of peritoneal macrophages gradually develop over a 3–4 d period the characteristic features of fibroblasts. These cells with time then develop filament bundles and a basal lamina to become myofibroblasts.