Increased vascular permeability in the thymus of the autoimmune New Zealand mouse

The thymus glands of non-autoimmune BDF1 and C3H mice and autoimmune NZB/WF1 mice were studied histologically at intervals ranging from one hour to 60 days after systemic administration of carbon. In NZB/WF1 mice over 9 weeks of age, many circulating carbon-laden macrophages were seen to have penetrated the walls of blood vessels, and to have then entered the thymic parenchyma. Carbon was also taken up by many perivascular macrophages stretched out along blood vessels and by many resident tissue macrophages scattered throughout the thymic parenchyma. In contrast, no carbon was seen at any time in the extravascular tissues of the thymus in BDF1 and C3H mice of comparable age. These results indicate a great increase in the permeability of blood vessels in the thymus of NZB/WF1 mice. This increase in carbon permeability occurs both in the cortex and the medulla, particularly at the corticomedullary junction. There is little increase in the permeability to carbon in NZB/WF1 mice at the age of 4 weeks, suggesting that the increase in vascular permeability begins between the ages of 4 and 9 weeks. The possible role of this greatly increased blood vessel permeability in the thymus on the aetiology and pathogenesis of autoimmune disease is discussed.