The migrant cells in allotransplants of heart, kidney and skin. 1. A comparative electron microscopic analysis of the migrant cells.

The cells migrating into allotransplants of heart, kidney and skin have been assessed by electron microscopy and related to the physiological activity of these organs recorded at the time of their removal. The migrant cells consisted of macrophages—arriving in the transplants either as early macrophages or monocytes, neutrophils, blast-like cells and erythrocytes. The proportions of these types to the total number of cells varied from one tissue to another and also from one area to another within any given transplant. The overall dominant cell was the macrophage. Owing to their enormous size gained in the course of maturation, the macrophages come to occupy most of the interstitial tissue space and appear to be carrying on their legitimate function of phagocytosis of damaged cells. The only cells which were phagocytosed were “self” erythrocytes and platelets which had become extravasated, and later damaged, in the interstitium along with other circulating blood cells as a result of increased vascular permeability. Macrophages undergoing pinocytosis were more common in heart than in kidney allotransplants but this indicates, in general, that the macrophages were phagocytosing soluble “self” particles contained in the protein-rich extravasated plasma. However, ruffled “angry” macrophages were as much a feature of skin autotransplants as any allotransplant which renders the regulation of pinocytosis even more complex and not just a response to “not-self”. There was no evidence which would support claims that lymphocytes caused direct parenchymal damage and so initiate acute rejection or that they are the most numerous cells to be found in allotransplants. The migrant cells are a consequence of an initial inflammatory reaction in allotransplants and not the cause of it. A physiological assessment of function points to a failure of afferent peripheral perfusion due to increased venular pressure as the cause of acute rejection in all allotransplants.