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Mercuric chloride induces in the Brown-Norway rat a biphasic autoimmune disease characterized initially by linear IgG deposits along the glomerular basement membrane followed later by granular IgG deposition. In the present study, anti-glomerular basement membrane antibodies and immune complex-like material were sequentially assessed in serial serum samples. Both were transiently found at the same period. Glomerular linear IgG deposits were present on day 11 but circulating anti-glomerular basement membrane antibodies were only found later on day 16. Circulating immune complexes were first detectable on day 8 before the earliest granular IgG deposits were first observed in the spleen vessels on day 16. The disappearance of circulating anti-glomerular basement membrane antibodies and of circulating immune complexes, although HgCl2 injections were pursued, is in agreement with the self-limited character of mercuric chloride induced autoimmune disease and suggests the induction of immunosuppressive mechanisms.

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The surface of the large cystic spaces and dilated blood vessels in seven cases of aneurysmal bone cysts was studied. The endothelium of the blood vessels was surrounded by a layer of collagen types IV and V, and the endothelial cells contained factor VIII related antigen demonstrated by the peroxidase anti-peroxidase technique. Some blood vessels were dilated resembling small aneurysmal spaces. The visible surfaces of the aneurysmal spaces were devoid of collagen types IV and V, and of factor VIII related antigen. Ultrastructural analysis of paraffin embedded sections did not show the characteristic fine structural features of endothelium covering the aneurysmal spaces. It is concluded that the large spaces in aneurysmal bone cysts are devoid of basement membranes and endothelial cells. The absence of endothelium may explain the abundance of haemorrhages in these lesions. Immunocytochemical demonstration of endothelial antigen provides a valuable tool for the differential diagnosis between aneurysmal bone cysts and vascular tumours.