Antigen copy number and antibody dose can determine the outcome of erythrocyte alloimmunization inducing either antibody-mediated immune suppression or enhancement in a murine model.

BACKGROUND: The administration of anti-D for the prevention of hemolytic disease of the fetus and newborn is one of the most successful clinical uses of the phenomenon of antibody-mediated immune suppression (AMIS). However, despite adequate prophylaxis, failures can still occur in the clinic and are poorly understood. Recently, the copy number of red blood cell (RBC) antigens has been shown to influence immunogenicity in the context of RBC alloimmunization; however, its influence on AMIS remains unexplored. STUDY DESIGN AND METHODS: RBCs expressing approximately 3,600 and approximately 12,400 copy numbers of surface-bound hen egg lysozyme (HEL), named respectively HELmed -RBCs and HELhi -RBCs, and selected doses of a polyclonal HEL-specific IgG were transfused into mice. Recipient HEL-specific IgM, IgG, and IgG subclass responses were evaluated by ELISA. RESULTS: Antigen copy number affected the antibody dose required for AMIS induction with higher antigen copy numbers requiring larger doses of antibody. For instance, 5 µg of antibody caused AMIS for HELmed -RBCs but not HELhi -RBCs, while 20 µg induced significant suppression for both HEL-RBCs. Overall, increasing amounts of the AMIS-inducing antibody were associated with a more complete AMIS effect. In contrast, the lowest tested doses of the AMIS-inducing IgG led to evidence of enhancement at the IgM and IgG levels. DISCUSSION: The results demonstrate that the relationship between antigen copy number and antibody dose can influence the outcome of AMIS. Further, this work suggests that the same antibody preparation can induce both AMIS and enhancement but that the outcome may depend on the quantitative interrelationship of antigen-antibody binding.