Background. Due to the absence of αGAL epitopes, humans and galactosyltransferase knock-out (GALT/KO) mice express high levels of anti- Gal antibodies. We describe the properties of mouse anti-GAL antibodies. Methods. Anti-GAL IgG antibodies were quantified by affinity purification. Antibody affinities and avidities were determined in direct binding and competition assays. Antibody-mediated rejection was investigated using hyperimmunized GALT/KO mice as recipients of GAL+ heart allografts. Results. In young GALT/KO mice the levels of anti-GAL antibodies were low. Immunization of GALT/KO mice resulted in increased anti-GAL antibody expression. In mouse serum 0.6% of IgG was specific for αGAL compared to 0.5% in human serum. The avidity of purified mouse and human anti-GAL IgG was 30 and 6 nM, the affinity 15 and 50 μM, respectively. The isotype distribution in mouse and human anti-GAL IgG appeared to be similar to the isotype distribution in normal sera. The affinity of mouse and human antiGAL IgM was 150 and 750 μM, respectively. Immunized GALT/KO recipients of GAL+ heart transplants rejected their grafts within 2 hr although nonimmunized GALT/KO mice retained their grafts for up to 6 days. Immunohistological examination of the rejected GAL+ hearts revealed massive deposition of IgM and IgG on endothelial cells of the graft with a concomitant deposition of complement. Conclusions. Our studies demonstrate that anti-GAL antibodies from immunized GALT/KO mice bind αGAL with an avidity/affinity similar to human anti-GAL antibodies and are able to induce hyperacute rejection of GAL+ heart allografts.
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