An update on the I blood group system.

CONCLUSIONS: This update of the I blood group system (Cooling L. Polylactosamines, there's more than meets the "Ii": a review of the I system. Immunohematology 2010;26:133-55) continues to show the Ii antigens to be increasingly recognized as important posttranslational modifiers regulating cell adhesion, signaling, differentiation, and cancer. Ii antigens can modulate the immune response through the galectin lattice, as well as influence specific protein-protein interactions. Changes in GCNT2 and I expression accompany stem cell differentiation and are associated with tumor progression in melanoma and breast and colon cancer. Regulation of GCNT2 expression varies between cell types and differentiation. In red blood cell differentiation, GCNT2 is regulated by methylation, microRNAs, and mitogen-activated protein kinase signaling pathways. Methylation and microRNAs also play a prominent role in altering GCNT2 expression in several epithelial cancers. In congenital cataracts, GCNT2 mutations may account for 4-6 percent of all cases. GCNT2 may be particularly susceptible to gene deletion and rearrangements due to the density of Alu-repeat elements.