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Title: Humans lack iGb3 due to the absence of functional iGb3-synthase: implications for NKT cell development and transplantation.
Austin Authors: Christiansen, Dale;Milland, Julie;Mouhtouris, Effie ;Vaughan, Hilary A;Pellicci, Daniel G;McConville, Malcolm J;Godfrey, Dale I;Sandrin, Mauro S 
Affiliation: Northern Health, Heidelberg, Victoria, Australia
Surgery (University of Melbourne)
Issue Date: 15-Jul-2008
Publication information: Plos Biology; 6(7): e172
Abstract: The glycosphingolipid isoglobotrihexosylceramide, or isogloboside 3 (iGb3), is believed to be critical for natural killer T (NKT) cell development and self-recognition in mice and humans. Furthermore, iGb3 may represent an important obstacle in xenotransplantation, in which this lipid represents the only other form of the major xenoepitope Galalpha(1,3)Gal. The role of iGb3 in NKT cell development is controversial, particularly with one study that suggested that NKT cell development is normal in mice that were rendered deficient for the enzyme iGb3 synthase (iGb3S). We demonstrate that spliced iGb3S mRNA was not detected after extensive analysis of human tissues, and furthermore, the iGb3S gene contains several mutations that render this product nonfunctional. We directly tested the potential functional activity of human iGb3S by expressing chimeric molecules containing the catalytic domain of human iGb3S. These hybrid molecules were unable to synthesize iGb3, due to at least one amino acid substitution. We also demonstrate that purified normal human anti-Gal immunoglobulin G can bind iGb3 lipid and mediate complement lysis of transfected human cells expressing iGb3. Collectively, our data suggest that iGb3S is not expressed in humans, and even if it were expressed, this enzyme would be inactive. Consequently, iGb3 is unlikely to represent a primary natural ligand for NKT cells in humans. Furthermore, the absence of iGb3 in humans implies that it is another source of foreign Galalpha(1,3)Gal xenoantigen, with obvious significance in the field of xenotransplantation.
DOI: 10.1371/journal.pbio.0060172
Journal: PLoS Biology
Type: Journal Article
Subjects: Amino Acid Substitution
Antigens, Heterophile.immunology
Cell Line
Cell Transplantation
Killer Cells, Natural.immunology
RNA Splicing
Transplantation, Heterologous.immunology
Appears in Collections:Journal articles

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