Nonhemolytic antigen loss from red blood cells requires cooperative binding of multiple antibodies recognizing different epitopes.

Transfusion of crossmatch-incompatible red blood cells (RBCs) can result in antibody-mediated hemolysis. However, in some patients, crossmatch-incompatible RBCs lose the incompatible antigen from their surface, and then circulate normally ("antigen loss"). Although antigen loss has been reported in the settings of autoimmune hemolytic anemia and transfusion of crossmatch-incompatible RBCs, mechanistic understanding of this phenomenon is limited. Using an in vivo murine model of antigen loss, we report that, unlike polyclonal antisera, monoclonal antibodies did not induce antigen loss. However, the combination of 2 monoclonal antibodies that recognized separate epitopes on the same antigen induced antigen loss. This was not due to an increased number of Fc domains bound to the cell surface, because antigen loss still occurred when combining intact monoclonal IgG and F(ab')2 fragments recognizing different epitopes. Together, these data lead to the hypothesis that antigen-antibody crosslinking is required for nonhemolytic antigen loss to occur.