RESUMO
Assays for quantification, and methods for removal, of anti-A and anti-B antibodies are the key for the success of ABO incompatible organ transplantation programs. In order to produce tools that can be used as substrates in tests for anti-A/anti-B quantification and specificity determination or as affinity matrices in extracorporeal immunoadsorption (IA) columns, we engineered Chinese hamster ovary (CHO) cells secreting mucin-type fusion proteins carrying blood group A or B determinants on defined O-glycan core saccharide chains. Besides the P-selectin glycoprotein ligand-1/mouse immunoglobulin G(2b) (PSGL-1/mIgG(2b)) cDNA, CHO cells were transfected with plasmids encoding core 2 (ß1,6GlcNAc-T1) or core 3 (ß1,3GlcNAc-T6 and ß1,3Gal-T5) enzymes together with α1,2Fuc-T1 or α1,2Fuc-T2 and the A or B gene-encoded α1,3GalNAcT or α1,3Gal-T, respectively. Selected clones with the correct glycophenotype were expanded and cultured in shaker flasks and Wave bioreactors. Western blotting was used to characterize purified fusion protein and liquid chromatography-mass spectrometry was used to characterize the released O-glycans. Clones producing PSGL-1/mIgG(2b) carrying O-glycans with A and B determinants on type 1 (Galß3GlcNAc), type 2 (Galß4GlcNAc) and type 3 (Galß3GalNAcα) outer core saccharide chains were established. The conversion of CHO cells from exclusive inner core 1 (Galß3GalNAc) to core 3 (GlcNAcß3GalNAc) O-glycan producers was almost complete, whereas conversion to inner core 2 (GlcNAcß6GalNAc) O-glycans was incomplete as was the α2-fucosylation of the core 1 chain. Sialylation may prevent these biosynthetic steps. The clinical utility of the blood group A and B substituted mucin-type fusion proteins as substrates in enzyme-linked immunosorbent assay or as affinity matrices in IA columns is explored.
Assuntos
Sistema ABO de Grupos Sanguíneos/biossíntese , Mucinas/biossíntese , Processamento de Proteína Pós-Traducional , Animais , Células CHO , Configuração de Carboidratos , Sequência de Carboidratos , Cromatografia de Afinidade , Cricetulus , Glicosilação , Imunoglobulina G/biossíntese , Técnicas de Imunoadsorção , Glicoproteínas de Membrana/biossíntese , Dados de Sequência Molecular , N-Acetilgalactosaminiltransferases/biossíntese , Proteínas Recombinantes de FusãoRESUMO
BACKGROUND: Antigen-specific removal of anti-A and anti-B on immunoadsorption columns carrying the blood group A and B trisaccharides is one important component of some protocols used in ABO-incompatible organ transplantation. Because ABO antibodies exist requiring parts of the core saccharide chain for binding, the anti-A and -B-binding capacity of individual and combined, Sepharose-linked Types 1 through 4 A and B tetrasaccharides with that of the A and B trisaccharides was compared. STUDY DESIGN AND METHODS: Sepharose-linked A and B tri- and tetrasaccharides were used to adsorb anti-A and -B from pooled blood group O serum. Remaining chain type-specific anti-A and -B were detected and quantified in enzyme-linked immunosorbent assays using wells coated with neoglycoproteins or recombinant mucins carrying A and B determinants on defined core saccharide chains. RESULTS: Significantly more anti-A Type 3- and 4-specific immunoglobulin (Ig)G remained after adsorption on the A trisaccharide and the A Type 1 and A Type 2 tetrasaccharide than after adsorption on the A Types 3 and 4 tetrasaccharides. Selective adsorption of chain type-specific IgG anti-B was detected on Sepharose-linked B tetrasaccharides. In contrast, there were no chain type-specific IgM anti-A or -B. A combination of the A or B tetrasaccharides adsorbed a larger fraction of the IgG anti-A and -B repertoires than the corresponding trisaccharides. CONCLUSION: There are chain type-specific anti-A and anti-B IgG, and an adsorber based on a combination of Types 1 through 4 A or B tetrasaccharides will be a more efficient adsorber than an adsorber based on the A or B trisaccharides.
Assuntos
Sistema ABO de Grupos Sanguíneos/imunologia , Anticorpos/isolamento & purificação , Técnicas de Imunoadsorção , Sefarose , Especificidade de Anticorpos , Tipagem e Reações Cruzadas Sanguíneas , Ensaio de Imunoadsorção Enzimática , Histocompatibilidade/imunologia , Humanos , Imunoglobulina G/isolamento & purificação , Imunoglobulina M/isolamento & purificação , Transplante de Rim/imunologia , Oligossacarídeos , Imunologia de TransplantesRESUMO
Mannose-binding proteins like the macrophage mannose receptor (MR), the dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) and mannose-binding lectin (MBL) play crucial roles in both innate and adaptive immune responses. Immunoglobulin fusion proteins of the P-selectin glycoprotein ligand-1 (PSGL-1/mIgG(2b)) carrying mostly O-glycans and, as a control, the α1-acid glycoprotein (AGP/mIgG(2b)) carrying mainly N-linked glycans were stably expressed in the yeast Pichia pastoris. Pichia pastoris-produced PSGL-1/mIgG(2b) was shown to carry O-glycans that mediated strong binding to mannose-specific lectins in a lectin array and were susceptible to cleavage by α-mannosidases including an α1,2- but not an α1,6-mannosidase. Electrospray ionization ion-trap mass spectrometry confirmed the presence of O-glycans containing up to nine hexoses with the penta- and hexasaccharides being the predominant ones. α1,2- and α1,3-linked, but not α1,6-linked, mannose residues were detected by (1)H-nuclear magnetic resonance spectroscopy confirming the results of the mannosidase cleavage. The apparent equilibrium dissociation constants for binding of PNGase F-treated mannosylated PSGL-1/mIgG(2b) to MR, DC-SIGN and MBL were shown by surface plasmon resonance to be 126, 56 and 16 nM, respectively. In conclusion, PSGL-1/mIgG(2b) expressed in P. pastoris carried O-glycans mainly comprised of α-linked mannoses and with up to nine residues. It bound mannose-specific receptors with high apparent affinity and may become a potent targeting molecule for these receptors in vivo.
Assuntos
Lectinas Tipo C/metabolismo , Lectinas de Ligação a Manose/metabolismo , Glicoproteínas de Membrana/química , Glicoproteínas de Membrana/metabolismo , Mucinas/biossíntese , Mucinas/química , Pichia/genética , Receptores de Superfície Celular/metabolismo , Proteínas Recombinantes de Fusão/biossíntese , Animais , Células CHO , Sequência de Carboidratos , Cricetinae , Cricetulus , Lectinas Tipo C/imunologia , Manose/química , Manose/metabolismo , Receptor de Manose , Lectinas de Ligação a Manose/imunologia , Glicoproteínas de Membrana/biossíntese , Glicoproteínas de Membrana/genética , Dados de Sequência Molecular , Mucinas/genética , Mucinas/metabolismo , Receptores de Superfície Celular/imunologia , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genéticaRESUMO
BACKGROUND: Hemagglutination for detection and semiquantification of ABO antibodies is associated with large center-to-center variations and poor reproducibility. Because acceptance for transplantation and diagnosis of rejection in ABO-incompatible transplantation rely on the levels and specificity of ABO antibodies, reproducible tests that allow their detection and specificity determination are required. STUDY DESIGN AND METHODS: The level of chain type-specific anti-A and anti-B were analyzed in the sera of 44 healthy individuals of known ABO blood group using an enzyme-linked immunosorbent assay (ELISA) with polyacrylamide (PAA) conjugates of blood group A and B trisaccharides or Type 2 chain A and B tetrasaccharides. Selected sera were further analyzed by hemagglutination and in an ELISA with Types 1 to 4 chain A or B neoglycolipids (NGL) as antigens. RESULTS: Immunoglobulin (Ig)G anti-A and anti-B levels were higher (p ≤ 0.05) in blood group O than in B and A individuals. More IgM anti-A and anti-B cross-reactivity was detected in AB serum on PAA-conjugated A and B trisaccharides than on the tetrasaccharides. One of 11 blood group B and two of 12 A individuals had IgG antibodies binding the tetrasaccharide despite lack of, or very low reactivity with, the trisaccharides. IgG antibodies preferring the A and B Type 2 tetrasaccharides were of the IgG2 subclass. The NGL ELISA further supported the presence of chain type-specific anti-A and -B antibodies among nonsensitized, healthy individuals. CONCLUSION: An ELISA with structurally defined ABH antigens will allow the antibody class and fine specificity of ABO antibodies to be determined, which may improve risk assessment in ABO-incompatible transplantation.
Assuntos
Sistema ABO de Grupos Sanguíneos/imunologia , Doadores de Sangue , Isoanticorpos/sangue , Sistema ABO de Grupos Sanguíneos/química , Incompatibilidade de Grupos Sanguíneos , Ensaio de Imunoadsorção Enzimática , Testes de Hemaglutinação , Humanos , Imunoglobulina G/sangueRESUMO
Metabolic engineering of mammalian cells for optimized glycosylation is usually done to improve activity and the pharmacokinetic features of glycoprotein therapeutics. The field is mainly focused around engineering of N-glycans. We have created a platform in which recombinant mucin-type immunoglobulin fusion proteins are used as scaffolds for multivalent expression of O-glycans with diagnostic or therapeutic potential. The methods used to make stable CHO cell lines secreting a mucin-type fusion protein with blood group A or B determinants following expression of up to five different cDNAs are described.