The migrant cells in allotransplants of heart, kidney and skin. III. The source and evolution of migrant cells in association with allotransplant fibroplasia

Abstract

A detailed electronmicroscopic assessment of the cells in the thoracic duct indicates that small lymphocytes do not monopolize the mononuclear cell content. Macrophages, eosinophils and many unidentified types make up about 50% of the cells and the remainder are either monocytes or lymphocytes which cannot be distinguished at certain stages by the electronmicroscope. The number of lymphocytes circulating in the peripheral blood has been radically reduced by recent electronmicroscopic assessments and their place taken by monocytes. Identification of cells in allotransplants has been mainly based on observed function such as phagocytosis, rather than on vague notions of lymphoid morphology before adequate differentiation has occurred. On this basis the migrant population contained few lympoid cells.

Cells similar to those circulating in the peripheral blood can be observed migrating continuously through the small vessels of the allotransplants and they are either immature phagocytes or evolving monocytes, as indicated by pinocytosis or phagocytosis. These are the cells which come to dominate the interstitial tissues of all allotransplants examined. In many areas the arrival of the macrophages coincides with stimulation of the allotransplant's own fibroblasts, which rapidly divide and enlarge and adhere to one another to such an extent that they dominate some areas of the interstitial space. The joint activity of the scavenging macrophages and the healing fibroblasts can best be interpreted as a conventional process aimed at repairing the damage resulting from the inflammatory vascular reaction by the allotransplants soon after being placed in a foreign circulation. The interstitial cell population of allotransplants is partly derived from the donor and partly from the recipient. No evidence has emerged which suggests that either cell type is in any way engaged in immunological activity or directly responsible for parenchymal damage.