A model of a blood vessel was constructed in vitro. Its multilayered structure resembled that of an artery and it withstood physiological pressures. Electron microscopy showed that the endothelial cells lining the lumen and the smooth muscle cells in the wall were healthy and well differentiated. The lining of endothelial cells functioned physically, as a permeability barrier, and biosynthetically, producing von Willebrand's factor and prostacyclin. The strength of the model depended on its multiple layers of collagen integrated with a Dacron mesh.

We have examined the interaction between sera from patients with myasthenia gravis and acetylcholine receptor (AcChoR) purified from normal and denervated rat skeletal muscles [junctional receptor (UR) and extrajunctional receptor (EJR), respectively]. Eight of ten myasthenic sera had titers against EJR that were significantly higher (1.1-2.4 times) than their titers against JR. The antireceptor titers of these sera ranged from 2 to 102 nM. Although activities of three other sera were too low (<1 nM) to allow accurate titrations, provisional measurements with these sera gave titers against EJR that were at least as high (1.0-1.4 times) as those against JR. Competition

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