Carbohydrate dependent adhesion of leukocytes and the role of fucosyltransferase VII

Sammanfattning: Galectins, E-and P-selectins are carbohydrate-binding proteins that are up regulated at inflammatory lesions. Selectins expressed ou the activated endothelium mediate transient binding to leukocyte ligands that require sequential action of α 2,3-sialyltransferases and a 1,3-fucosyltransferases. ln leukocytes α1,3 fucosyltransferase VII adds fucose to α 2,3- sialylated lactosarnine acceptors in the final step of the biosynthesis of the selectin binding epitope sialyl Lewis x.The finding of low sialyl Lewis x expression in polymorphonuclear leukocytes from a patient with ulcerative colitis led to the discovery of a missense mutation (G329A) in the human gene coding for α1,3 fucosyltransferase VII, FUT7. Studies including enzymatic and immunochemical analysis oftransfected cell lines and isolated polymorphonuclear leukocytes from patients confirmed that this mutation impair the ability of α1,3 fucosyltransferase VII to synthesize sialyl Lewis x. The frequency of the mutation were measured in a mixed Swedish population and found to be -1 %. One individual carrying the FUT7-G329A mutation homozygously was identified. This individual suffered from ulcer disease, noninsulin-dependent diabetes, osteoporosis, spondyloarthrosis, and Sjögren's syndrome, but the relationship between disease and the mutation is not established.Studies using an in vitro flow chamber assay showed that transfected B-lymphoma cells and Epstein-Barr virus transformed B cells only transcribing FUT7-G329A were not able to interact with E-selectin during flow whereas polymorphonuclear leukocytes from the FUT7-G329A homozygous individual interacted well with both P- and E selectin during flow. The mRNA level of the fucosyltransferase IV coding gene, FUT4, was found to be elevated in the homozygous individual, which resulted in elevated levels ofthe CD65s epitope. However, transfected B-lymphoma cells and Epstein- Barr virus transformed cells did not show a similar elevation of FUT4 mRNA. In in vitro studies galectin-1 and- 3 were observed to be able to recruit polymorphonuclear leukocytes during flow. This thesis gives further insight into the molecular mechanisms leading to carbohydrate dependent dynamic adhesion between polymorphonuclear leukocytes and lectins during inflammation.