Avidin attachment to red blood cells via a phospholipid derivative of biotin provides complement-resistant immunoerythrocytes.

Preincubation of red blood cells (RBC) in an aqueous dispersion of biotin-phosphatidylethanolamine (biotin-PE) provides binding sites for avidin on the surface of these cells (up to 5 x 10(5) avidin molecules per cell). Previously we have shown that biotin covalently attached to the surface of RBC by a chemical reaction with biotin N-hydroxysuccinimide ester permits attachment of avidin to these cells, resulting in the activation of the alternative pathway of complement with subsequent cell lysis. However, avidin attached to RBC via biotin-PE did not cause complement activation. This is not due to the stabilizing action of biotin-PE. In contrast, various phospholipids, including biotin-PE, enhance the lysis of RBC induced by hemolytic antibodies via the classical complement pathway. The potential of avidin-coated RBC to act as activators of the complement alternative pathway depends on the method of biotin attachment to RBC. Complement-resistant avidin-coated RBC can specifically bind biotinylated antibodies. These immunoerythrocytes effectively and specifically bind to the antigen-coated surface and are not lysed by complement even in the presence of soluble antigen. These data extend the possible applications of immunoerythrocytes in drug targeting.