Sinusoidal endothelium in mouse liver show rapid and saturable binding of Jo2 anti-Fas antibody

To evaluate liver binding of Jo2, a Fas agonist antibody known to induce death in mice. Jo2 was labeled with 99mTc and separately conjugated with Cy5.5. Following dosing in normal and Fas deficient mice, the in vivo distribution of 99mTc-Jo2 was imaged. Biodistribution studies were conducted, and liver sections from mice injected with Cy5.5-Jo2 were immunostained with endothelial-specific antibodies and examined by confocal microscopy. 99mTc-Jo2 injected intravenously (i.v.) was rapidly bound in the mouse liver. Fas dependence was confirmed by reduced liver binding in Fas deficient mice. For intraperitoneal (i.p.) dosing, the liver binding was delayed. However, tissue distributions were similar for both routes of injection. 99mTc-Jo2 liver binding was saturated at greater than 10 μg. For Cy5.5-Jo2 doses less than 10 μg, binding within the liver was confirmed to be sinusoidal endothelium. Rapid binding of Jo2 to liver endothelium is the initial event of Jo2-induced death.