Response to Milland et al. : Carbohydrate residues downstream of the terminal Galα(1,3)Gal epitope modulate the specificity of xenoreactive antibodies

Zhou and Levery raise several issues related to our work1 that we would like to address. First, these authors are concerned with the specificity of the mAb 15.101. In the first paragraph of page 627, we state ‘Thus, we can conclude that all the mAbs can bind to Galα(1,3)Gal antigens produced by α1,3GT (protein and lipid) and iGb3S (lipid) on the cell surface. However, of all the antibodies studied, 15.101 binds cell surface expressed Galα(1,3)Gal produced by α1,3GT only weakly, whereas it binds intensely to Galα(1,3)Gal produced by iGb3S (that is, iGb3).’ Zhou and Levery criticize the claim that 15.101 can indeed identify iGb3. They correctly state that iGb3 synthase (iGb3S), the enzyme that generates iGb3, also produces poly-α-Gal glycosphingolipids (GSL) using iGb3, Gb3, iGb4 and Gb4 as substrates.2, 3 We have published data that clearly show that the mAb 15.101 does indeed bind to purified iGb3 in ELISA assays.4 Furthermore, we have thin layer chromatography data showing 15.101 binding to both iGb3 and poly-α-Gal GSL (data not shown). Thus, this mAb can detect all forms of Galα(1,3)Gal produced by iGb3S. Accordingly, we should have stated ‘binds intensely to Galα(1,3)Gal produced by iGb3S (including iGb3).’