Specific binding of rB19ECP to Ku80. (A) Specific binding of Ku80 to rB19ECP. Indicated concentration of biotinylated rKu80 or biotinylated BSA was reacted with rB19ECP fixed to 96 microwells and detected by ELISA. (B) Competitive ELISA for rB19ECP binding to rKu80. Biotinylated rKu80 (2 μg/mL) was reacted with rB19ECP fixed to wells in the presence of indicated doses of unlabeled rKu80, rKu70, sCD26, or globoside. (C) Inhibition of rB19ECP binding to rKu80 by purified B19. Biotinylated rKu80 (1 μg/mL) was added to rB19ECP fixed to wells in the presence of B19 that was purified from B19⁺ serum with repeated microfiltration. Doses of B19 are expressed as copy numbers of B19 DNA. (D) Inhibition of rB19ECP binding to rKu80 by anti-Ku80 antibodies. Binding of biotinylated rKu80 or biotinylated BSA to rB19ECP fixed to wells was measured in the presence of isotype-matched mouse monoclonal antibodies as indicated.