Anti-GAL antibodies in humans and 1,3α-galactosyltransferase knock-out mice

Background. Due to the absence of alpha GAL 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 alpha GAL 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 mu M, 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 anti-GAL IgM was 150 and 750 mu M, 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 alpha GAL with an avidity/affinity similar to human anti-GAL antibodies and are able to induce hyperacute rejection of GAL(+) heart allografts.