title: C8 binding protein bears I antigenic determinants.
abstract: C8 binding protein (C8bp) is an integral membrane glycoprotein of peripheral blood cells, which inhibits the C5b-9-mediated lysis in a homologous system. In the present study, we analyzed the carbohydrate portion of the C8bp. We found that C8bp is associated with I antigenic determinant, a sugar sequence found on human erythrocytes of adults. To assess whether or not the sugar residues are essential for the C8bp function, I determinant was cleaved off from the isolated C8bp by endo-beta-galactosidase (E.C. 3.2.2.103) that hydrolyses internal beta-galactosidic-linked-N-acetyllactosamine residues. Enzyme treatment removed I-antigen, the inhibitory function of C8bp, however, was not affected. When intact erythrocytes were treated with endo-beta-galactosidase, I-antigen was lost and the lytic insusceptibility of human erythrocytes to homologous C5b-9 could not be abolished. Thus, I-antigen is associated with the C8bp, but its presence is not required for the homologous species restriction.
authors.affiliation: Institut für Immunologie der Universität Heidelberg, Federal Republic of Germany.
authors.forename: P
authors.initials: P
authors.lastname: Blaas-Mautner
authors.forename: S
authors.initials: S
authors.lastname: Filsinger
authors.forename: B
authors.initials: B
authors.lastname: Berger
authors.forename: D
authors.initials: D
authors.lastname: Roelcke
authors.forename: G M
authors.initials: GM
authors.lastname: Hänsch
mesh_terms: D001798:Blood Proteins / Q000737:chemistry / Q000276:immunology* / Q000502:physiology; D018957:CD59 Antigens; D002240:Carbohydrate Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000276:immunology* / Q000502:physiology; D004912:Erythrocytes / Q000276:immunology / Q000378:metabolism*; D006026:Glycoside Hydrolases; D006461:Hemolysis; D006801:Humans; D007048:I Blood-Group System / Q000502:physiology*; D008969:Molecular Sequence Data; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D018957:CD59 Antigens; D002352:Carrier Proteins; D007048:I Blood-Group System; C051590:CD59 protein, human; D006026:Glycoside Hydrolases; C026093:keratan-sulfate endo-1,4-beta-galactosidase; D001616:beta-Galactosidase