The structures of glycophorin C N-glycans, a putative component of the GPC receptor site for Plasmodium falciparum EBA-140 ligand.

Glycophorins C and D are highly glycosylated integral sialoglycoproteins of human red blood cell membranes carrying the Gerbich blood group antigens. The O- and N-glycosidic chains of the major erythrocyte glycoprotein (Lisowska E. 2001, Antigenic properties of human glycophorins - an update. Adv Exp Med Biol, 491:155-169; Tomita M and Marchesi VT. 1975, Amino-acid sequence and oligosaccharide attachment sites of human erythrocyte glycophorin. Proc Natl Acad Sci USA, 72:2964-2968.) are well characterized but the structure of GPC N-glycans has remained unknown. This problem became important since it was reported that GPC N-glycans play an essential role in the interaction with Plasmodium falciparum EBA-140 merozoite ligand. The elucidation of these structures seems essential for full characterization of the GPC binding site for the EBA-140 ligand. We have employed detailed structural analysis using sequential mass spectrometry to show that many GPC N-glycans contain H2 antigen structures and several contain polylactosamine structures capped with fucose. The results obtained indicate structural heterogeneity of the GPC N-glycans and show the existence of structural elements not found in glycophorin A N-glycans. Our results also open a possibility of new interpretation of the data concerning the binding of P. falciparum EBA-140 ligand to GPC. We hypothesize that preferable terminal fucosylation of N-glycosidic chains containing repeating lactosamine units of the GPC Gerbich variant could be an explanation for why the EBA-140 ligand does not react with GPC Gerbich and an indication that the EBA-140 interaction with GPC is distinctly dependent on the GPC N-glycan structure.

A single point mutation in the gene encoding Gb3/CD77 synthase causes a rare inherited polyagglutination syndrome.

Rare polyagglutinable NOR erythrocytes contain three unique globoside (Gb4Cer) derivatives, NOR1, NOR(int), and NOR2, in which Gal(α1-4), GalNAc(ß1-3)Gal(α1-4), and Gal(α1-4)GalNAc(ß1-3)Gal(α1-4), respectively, are linked to the terminal GalNAc residue of Gb4Cer. NOR1 and NOR2, which both terminate with a Gal(α1-4)GalNAc- sequence, react with anti-NOR antibodies commonly present in human sera. While searching for an enzyme responsible for the biosynthesis of Gal(α1-4)GalNAc, we identified a mutation in the A4GALT gene encoding Gb3/CD77 synthase (α1,4-galactosyltransferase). Fourteen NOR-positive donors were heterozygous for the C>G mutation at position 631 of the open reading frame of the A4GALT gene, whereas 495 NOR-negative donors were homozygous for C at this position. The enzyme encoded by the mutated gene contains glutamic acid instead of glutamine at position 211 (substitution Q211E). To determine whether this mutation could change the enzyme specificity, we transfected a teratocarcinoma cell line (2102Ep) with vectors encoding the consensus Gb3/CD77 synthase and Gb3/CD77 synthase with Glu at position 211. The cellular glycolipids produced by these cells were analyzed by flow cytometry, high-performance thin-layer chromatography, enzymatic degradation, and MALDI-TOF mass spectrometry. Cells transfected with either vector expressed the P1 blood group antigen, which was absent from untransfected cells. Cells transfected with the vector encoding the Gb3/CD77 synthase with Glu at position 211 expressed both P1 and NOR antigens. Collectively, these results suggest that the C631G mutation alters the acceptor specificity of Gb3/CD77 synthase, rendering it able to catalyze synthesis of the Gal(α1-4)Gal and Gal(α1-4)GalNAc moieties.

ABH blood group antigens in N-glycan of human glycophorin A.

We previously showed that a small proportion of the O-linked oligosaccharide chains of human glycophorin A (GPA) contains blood group A, B or H antigens, relevant to the ABO phenotype of the donor. The structures of these minor O-glycans have been established (Podbielska et al. (2004) [20]). By the use of immunochemical methods we obtained results indicating that ABH blood group epitopes are also present in N-glycan of human GPA (Podbielska and Krotkiewski (2000) [22]). In the present paper we report a detailed analysis of GPA N-glycans using nanoflow electrospray ionization tandem mass spectrometry. N-glycans containing A-, B- and H-related sequences were identified in GPA preparations obtained from erythrocytes of blood group A, B and O donors, respectively. The ABH blood group epitopes are present on one antenna of the N-glycan, whereas a known sialylated sequence NeuAcalpha2-6Galbeta1-4GlcNAc- occurs on the other antenna and other details are in agreement with the known major structure of the GPA N-glycan. In the bulk of the biantennary sialylated N-glycans released from GPA preparations, the blood group ABH epitopes-containing N-glycans, similarly O-glycans, constituted only a minor part. The amount relative to other N-glycans was estimated to 2-6% of blood group H epitope-containing glycans released from GPA-O preparations and 1-2% of blood group A and B epitope-containing glycans, released from GPA-A and GPA-B, respectively.

Lectins as tools in glycoconjugate research.

Lectins are ubiquitous proteins of nonimmune origin, present in plants, microorganisms, animals and humans which specifically bind defined monosugars or oligosaccharide structures. Great progress has been made in recent years in understanding crucial roles played by lectins in many biological processes. Elucidation of carbohydrate specificity of human and animal lectins is of great importance for better understanding of these processes. Long before the role of carbohydrate-protein interactions had been explored, many lectins, mostly of plant origin, were identified, characterized and applied as useful tools in studying glycoconjugates. This review focuses on the specificity-based lectin classification and the methods of measuring lectin-carbohydrate interactions, which are used for determination of lectin specificity or for identification and characterization of glycoconjugates with lectins of known specificity. The most frequently used quantitative methods are shortly reviewed and the methods elaborated and used in our laboratories, based on biotinylated lectins, are described. These include the microtiter plate enzyme-linked lectinosorbent assay, lectinoblotting and lectin-glycosphingolipid interaction on thin-layer plates. Some chemical modifications of lectin ligands on the microtiter plates and blots (desialylation, Smith degradation, beta-elimination), which extend the applicability of these methods, are also described.

Murine monoclonal anti-s and other anti-glycophorin B antibodies resulting from immunizations with a GPB.s peptide.

BACKGROUND: The blood group antigens S and s are defined by amino acids Met or Thr at position 29, respectively, on glycophorin B (GPB). Commercial anti-s reagents are expensive to produce because of the scarcity of human anti-s serum. Our aim was to develop hybridoma cell lines that secrete reagent-grade anti-s monoclonal antibodies (MoAbs) to supplement the supply of human anti-s reagents. STUDY DESIGN AND METHODS: Mice were immunized with the GPB(s) peptide sequence TKSTISSQTNGETGQLVHRF. Hybridomas were produced by fusing mouse splenocytes with mouse myeloma cells (X63.Ag8.653). Screening for antibody production was done on microtiter plates by hemagglutination. Characterization of the MoAbs was done by hemagglutination, immunoblotting, and epitope mapping. RESULTS: Eight immunoglobulin G MoAbs were identified. Five antibodies are specific by hemagglutination for s and two MoAbs, when diluted, are anti-S-like, but additional analyses shows a broad range of reactivity for GPB. Typing red blood cells (RBCs) for s from 35 donors was concordant with molecular analyses as were tests on RBCs with a positive direct antiglobulin test (DAT) from 15 patients. The anti-s MoAbs are most reactive with peptides containing the (31)QLVHRF(36) motif, with (29)Thr. By Pepscan analyses, the anti-S-like MoAbs reacted within the same regions as did anti-s, but independently of (29)Met. One antibody was defined serologically as anti-U; however, its epitope was identified as (21)ISSQT(25), a sequence common for both GPA and GPB. CONCLUSION: In addition to their value as typing reagents, these MoAbs can be used to phenotype RBCs with a positive DAT without pre-test chemical modification.

Adhesive properties of carcinoembryonic antigen glycoforms expressed in glycosylation-deficient Chinese hamster ovary cell lines.

Carcinoembryonic antigen (CEA) is an oncofoetal cell surface glycoprotein that serves as an important tumour marker for colorectal and some other carcinomas. Its immunoglobulin-like structure places CEA within the immunoglobulin superfamily. CEA functions in several biological roles including homotypic and heterotypic (with other CEA family members) cell adhesion. Cell-cell interaction can be modulated by different factors, e.g., post-translational modifications such as glycosylation. The purpose of this study was to examine whether changes in carbohydrate composition of CEA oligosaccharides can influence homotypic (CEA-CEA) interactions. In order to modulate glycosylation of CEA we used two different glycosylation mutants of Chinese hamster ovary (CHO) cells, Lec2 and Lec8. Lec2 cells should produce CEA with nonsialylated N-glycans, while Lec8 cells should yield more truncated sugar structures than Lec2. Parental CHO (Pro5) cells and the glycosylation deficient mutants were stably transfected with CEA cDNA. All three CEA glycoforms, tested in a solid-phase cell adhesion assay, showed an ability to mediate CEA-dependent cell adhesion, and no qualitative differences in the adhesion between the glycoforms were observed. Thus, it may be assumed that carbohydrates do not play a role in homotypic adhesion, and the interactions between CEA molecules depend solely on the polypeptide structure.

Analysis of recombinant Duffy protein-linked N-glycans using lectins and glycosidases.

Duffy antigen is a glycosylated blood group protein acting as a malarial and chemokine receptor. Using glycosylation mutants we have previously demonstrated, that all three potential glycosylation sites of the Duffy antigen are occupied by N-linked oligosaccharide chains. In this study, wild-type Duffy glycoprotein and three mutants, each containing a single N-glycan, were used to characterize the oligosaccharide chains by lectin blotting and endoglycosidase digestion. The positive reaction of all the recombinant Duffy forms with Datura stramonium and Sambucus nigra lectins showed that each Duffy N-linked glycan contains Galbeta1-4GlcNAc units terminated by (alpha2-6)-linked sialic acid residues, typical of complex oligosaccharides. The reactivity with Aleuria aurantia and Lens culinaris lectins suggested the presence of (alpha1-6)-linked fucose at the N-glycan chitobiose core. The failure of the Galanthus nivalis and Canavalia ensiformis lectins to bind to any of the Duffy mutants or to the wild-type antigen indicated that none of the three Duffy N-glycosylation sites carries detectable levels of high-mannose oligosaccharide chains. Digestion of Duffy samples with peptide N-glycosidase F and endoglycosidase H confirmed the presence of N-linked complex oligosaccharides. Our results indicate that Duffy antigen N-glycans are mostly core-fucosylated complex type oligosaccharides rich in N-acetyllactosamine and terminated by (alpha2-6)-linked sialic acid residues.

Structures of unique globoside elongation products present in erythrocytes with a rare NOR phenotype.

Rare polyagglutinable erythrocytes of NOR phenotype were found to contain two unique glycosphingolipids (designated NOR1 and NOR2). These components (not detected in normal erythrocytes) were reactive with Griffonia simplicifolia isolectin IB4 (GSL-IB4) and commonly present human anti-NOR antibodies. The NOR1 component has been reported to be a globoside containing a single galactose residue linked alpha1,4 to the terminal N-acetylgalactosamine. Here, we report the structural studies on a second glycolipid, NOR2, and a third novel component migrating in high-performance thin-layer chromatography (HPTLC) between NOR1 and NOR2. The structures were determined by a combination of ion trap sequential mass spectrometry (MALDI-QIT-TOF) and step-wise treatment with glycosidases, followed by identification of products on HPTLC plates with lectins and mouse monoclonal anti-NOR antibody. The NOR2 component was found to be a disaccharide extension of NOR1 with the following structure: Galalpha1-4GalNAcbeta1-3Galalpha1-4GalNAcbeta1-3Galalpha1-4Galbeta1-4Glcbeta1-Cer. Treatment of NOR2 with alpha-galactosidase gave a glycolipid migrating between NOR1 and NOR2, which did not react with either GSL-IB4 or anti-NOR antibodies but did react with GalNAc-specific soybean agglutinin. This intermediate glycolipid (now designated NOR(int)) was identified as a relatively abundant component of a neutral glycolipid fraction from NOR erythrocytes, suggesting its presence as a precursor to NOR2. The structure of NOR(int) was also confirmed by sequential mass spectrometry studies. These results indicate that polyagglutination in NOR subjects is due to unique erythrocyte glycolipids that are synthesized by sequential addition of Galalpha1,4 and GalNAcbeta1,3 to globoside.

Presence of natural anti-Galalpha1-4GalNAcbeta1-3Gal (anti-NOR) antibodies in animal sera.

Rare polyagglutinable NOR erythrocytes contain unusual globoside extention products terminating with a Galalpha1-4GalNAcbeta1-3Gal- unit. This trisaccharide epitope is recognized by recently characterized antibodies naturally occurring in most human sera (Duk et al., Glycobiology, 15, 109, 2005). These antibodies represent two major types of fine specificity. All these antibodies are most strongly inhibited by Galalpha1-4GalNAcbeta1-3Gal (NOR-tri), and weakly by Galalpha1-4Gal. However, the type 1 antibodies are strongly inhibited by Galalpha1-4Galbeta1-3Gal-R and weakly by Galalpha1-4GalNAc, while the type 2 antibodies show the opposite reactivities with these two oligosaccharides. Similar antibodies have now been found in horse, rabbit and pig sera. The antibodies were purified from animal sera by affinity chromatography on Galalpha1-4GalNAcbeta1-3Gal-human serum albumin(HSA)-Sepharose 4B conjugate. The specificity of the antibodies was determined by binding to ELISA plates coated with several alpha-galactosylated oligosaccharide-polyacrylamide (PAA) or -HSA conjugates and by inhibition with synthetic oligosaccharides. The purified antibodies bound specifically to conjugates containing NOR-tri. The inhibition of binding showed that the animal sera also contain two types of anti-NOR antibodies: type 2 was found in the horse serum, and a mixture of both types was present in rabbit and pig serum. These results indicate that anti-NOR, a new and distinct kind of anti-alphaGal antibody, are present in animal sera and show similar specificties and diversity as their counterparts found in human sera.

Galactosylation of IgG from rheumatoid arthritis (RA) patients--changes during therapy.

It is well documented that serum IgG from rheumatoid arthritis (RA) patients exhibits decreased galactosylation of its conservative N-glycans (Asn-297) in CH2 domains of the heavy chains; it has been shown that this agalactosylation is proportional to disease severity. In the present investigation we analyzed galactosylation of IgG derived from the patients using a modified ELISA-plate test, biosensor BIAcore and total sugar analysis (GC-MS). For ELISA and BIAcore the binding of IgG preparations, purified from the patients' sera, to two lectins: Ricinus communis (RCA-I) and Griffonia simplicifolia (GSL-II) was applied. Based on ELISA-plate test an agalactosylation factor (AF, a relative ratio of GSL-II/RCA-I binding) was calculated, which was proportional to actual disease severity. Repeated testing of several patients before and after treatment with methotrexate (MTX) alone or in combination with Remicade (a chimeric antibody anti-TNF-alpha) supplied results indicating an increase of IgG galactosylation during the treatment. This introductory observation suggests that IgG galactosylation may be an additional indicator of the RA patients' improvement.

Anti-alpha-galactosyl antibodies recognizing epitopes terminating with alpha1,4-linked galactose: human natural and mouse monoclonal anti-NOR and anti-P1 antibodies.

The rare NOR erythrocytes, which are agglutinated by most human sera, contain unique glycosphingolipids (globoside elongation products) terminating with the sequence Galalpha1-4GalNAcbeta1-3Gal- recognized by common natural human antibodies. Anti-NOR antibodies were isolated from several human sera by affinity procedures, and their specificity was tested by inhibition of antibody binding to NOR-tri-polyacrylamide (PAA) conjugate (ELISA) by the synthetic oligosaccharides, Galalpha1-4GalNAcbeta1-3Gal (NOR-tri), Galalpha1-4GalNAc (NOR-di), Galalpha1-4Galbeta1-3Galbeta1-4Glc ((Gal)3Glc), and Galalpha1-4Gal (P1-di). Two major types of subspecificity of anti-NOR antibodies were found. Type 1 antibodies were found to react strongly with (Gal)3Glc and NOR-tri and weakly with P1-di and NOR-di, which indicated specificity for the trisaccharide epitope Galalpha1-4Gal/GalNAcbeta1-3Gal. Type 2 antibodies were specific to Galalpha1-4GalNAc, because they were inhibited most strongly by NOR-tri and NOR-di and were not (or very weakly) inhibited by (Gal)3Glc and P1-di. Monoclonal anti-NOR antibodies were obtained by immunizing mice with NOR-tri-human serum albumin (HSA) conjugate and were found to have type 2 specificity. All anti-NOR antibodies reacted specifically with NOR glycolipids on thin-layer plates. The cross-reactivity of type 1 anti-NOR antibodies with Galalpha1-4Gal drew attention to a possible antigenic relationship between NOR and blood group P system glycolipids. The latter glycolipids include Pk (Galalpha1-4Galbeta1-4Glc-Cer) present in all normal erythrocytes and P1 (Galalpha1-4Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc-Cer) present only in P1 erythrocytes. Sera of some P2 (P1-negative) persons contain natural anti-P1 antibodies. This prompted us to test the specificity of anti-P1 antibodies. Natural human anti-P1 isolated from serum of P2 individual and mouse monoclonal anti-P1 were best inhibited by Galalpha1-4Galbeta1-4GlcNAc (P1-tri) and did not react with NOR-tri and NOR-di. Monoclonal anti-P1 bound to Pk and P1 glycolipids and not to NOR glycolipids. These results indicated an entirely different specificity of anti-NOR and anti-P1 antibodies. Human serum samples differed in the content of anti-alpha-galactosyl antibodies, including both types of anti-NOR. In the sera of some individuals, type 1 or type 2 anti-NOR antibodies dominated, and other samples contained mixtures of both types of anti-NOR. The biological significance of these new abundant anti-alpha-galactosyl antibodies still awaits elucidation.

Construction of dimeric F(ab) useful in blood group serology.

BACKGROUND: When expressed in Escherichia coli, recombinant F(ab) contain a heavy-chain Fd fragment and a complete light-chain fragment. Because these F(ab) are monovalent, their avidity is significantly lower than that of a corresponding bivalent IgG antibody. In addition, when monovalent F(ab) are used in hemagglutination assays, antiglobulin reagents are required. Therefore, it would be useful to develop a system that expresses recombinant bivalent F(ab) in E. coli. STUDY DESIGN AND METHODS: Three modified vectors were constructed. Each contained cDNA sequences encoding a peptide linked to the C terminus of a heavy-chain CH1 region: an IgG1 hinge region (Hinge), a leucine zipper (Zip), or a peptide containing the Hinge and Zip sequences in tandem (HingeZip). The vectors were used to express two cloned F(ab) recognizing human antigens M and N: NNA7 (anti-N) and 425/2B (anti-M). The recombinant proteins were expressed in E. coli and were purified and evaluated by ELISA and hemagglutination. RESULTS: By gel filtration chromatography, 35, 90, and 70 percent of the purified F(ab) expressing the Hinge, Zip, and HingeZip tails, respectively, were dimers. By ELISA, the avidity of F(ab) containing the Zip or HingeZip tails was six to eight times higher than that of the corresponding monovalent F(ab). In addition, the dimeric F(ab) directly agglutinated RBCs in concentrations similar to those of corresponding bivalent IgG antibodies. CONCLUSIONS: An introduction of dimer-inducing peptides allowed the isolation of bacterially produced, bivalent F(ab). This approach could be useful for obtaining inexpensive, serologic reagents that may replace or complement conventional MoAbs produced by mammalian tissue culture methods.

Specificity of human anti-NOR antibodies, a distinct species of "natural" anti-alpha-galactosyl antibodies.

Natural anti-NOR antibodies are common in human sera and agglutinate human erythrocytes of a rare NOR phenotype. The NOR phenotype-related antigens are unique neutral glycosphingolipids recognized by these antibodies and Griffonia simplicifolia IB4 isolectin (GSL-IB4). The oligosaccharide chains of NOR glycolipids are terminated by Galalpha1-4GalNAcbeta1-3Galalpha units. To characterize the specificity of anti-NOR antibodies and compare it with specificities of GSL-IB4 and known anti-Galalpha1,3Gal antibodies, alpha-galactosylated saccharides and saccharide-polyacrylamide conjugates were used. New synthetic oligosaccharides, corresponding to the terminal di- and trisaccharide sequence of NOR glycolipids and the conjugate of the NOR-tri with HSA were included. These compounds were tested by microtiter plate ELISA and hemagglutination inhibition. Anti-NOR antibodies reacted most strongly with Galalpha1-4GalNAcbeta1-3Gal (NOR-tri), and over 100 times less strongly with Galalpha1-4GalNAc (NOR-di). The antibodies reacted also with Galalpha1-4Gal and Galalpha1-4Galbeta1-4GlcNAc, similarly as with NOR-di but not with other tested compounds. In turn, anti-Galalpha1,3Gal antibodies reacted most strongly with Galalpha1-3Gal and were very weakly inhibited by the NOR-related oligosaccharides (weaker than by galactose), and NOR-tri was less active than NOR-di. GSL-IB4 reacted with all tested alpha-galactosylated saccharides and conjugates, including the similarly active NOR-tri and NOR-di. These results showed that anti-NOR represent a new species of anti-alpha-galactosyl antibodies with high affinity for the Galalpha1-4GalNAcbeta1-3Gal sequence present in rare NOR erythrocytes.

The Fya, Fy6 and Fy3 epitopes of the Duffy blood group system recognized by new monoclonal antibodies: identification of a linear Fy3 epitope.

Four new anti-Duffy murine monoclonal antibodies (MAbs): two anti-Fy6 (MIMA-107 and MIMA-108), one anti-Fya (MIMA-19) and one anti-Fy3 (MIMA-29) were characterized. Identification of epitopes by means of synthetic peptides (Pepscan) showed that the anti-Fy6 reacted most strongly with peptides containing the sequence 19QLDFEDV25 of the Duffy glycoprotein, and less strongly with peptides containing LDFEDV (MIMA-107) or LDF only (MIMA-108). The anti-Fya recognized epitope 38DGDYGA43 containing the Gly42 residue, which defines the Fya blood group antigen. MIMA-29 is the first anti-Fy3 reactive with a linear epitope 281ALDLL285 located in the fourth extracellular domain (ECD4, loop 3) of the Duffy glycoprotein. The four new antibodies extend the list of six anti-Fy MAbs formerly characterized by Pepscan analysis that allow some general conclusions. Fine specificities of various anti-Fya, or anti-Fy6 are not identical, but all of them recognize linear epitopes located around, respectively, Gly42 or between two potential N-glycosylation sites at Asn16 and Asn27. Anti-Fy3 recognize either a linear epitope located in ECD4, or a conformational epitope that includes amino acid residues of ECD4 and of other ECDs.

ABH blood group antigens in O-glycans of human glycophorin A.

The major O-linked oligosaccharide structures attached to human glycophorin A (GPA) have been extensively characterized previously. Our own recent findings, obtained by immunochemical methods, suggested the presence of blood group A and B determinants in O-glycans of human glycophorin originating from blood group A or B erythrocytes, respectively. Here, we elucidate the structure of O-glycans, isolated from GPA of blood group A, B, and O individuals by reductive beta-elimination, carrying A, B or H blood group epitopes, respectively. Structural studies based on nanoflow electrospray-ionization tandem mass spectrometry and earlier reported data on the carbohydrate moiety of GPA and ABH antigens allowed us to conclude that these blood group epitopes are elongations of the beta-GlcNAc branch attached to C-6 of the reducing GalNAc. The galactose linked to C-3 of the reducing GalNAc carries NeuAcalpha2-3 linked residue. Identified here O-glycans were found in low amounts, their content estimated at about one percent of all GPA O-glycans. These O-glycans with type-2 core, carrying the blood group A, B or H determinants, have not been identified in GPA so far. Our results demonstrate the efficacy of nanoESI MS/MS in detecting minor oligosaccharide components present in a mixture with much more abundant structures.

Structure-function analysis of the extracellular domains of the Duffy antigen/receptor for chemokines: characterization of antibody and chemokine binding sites.

The Duffy antigen/receptor for chemokines (DARC), a seven-transmembrane glycoprotein carrying the Duffy (Fy) blood group, acts as a widely expressed promiscuous chemokine receptor. In a structure-function study, we analysed the binding of chemokines and anti-Fy monoclonal antibodies (mAbs) to K562 cells expressing 39 mutant forms of DARC with alanine substitutions spread out on the four extracellular domains (ECDs). Using synthetic peptides, we defined previously the Fy6 epitope (22-FEDVW-26), and we characterized the Fya epitope as the linear sequence 41-YGANLE-46. In agreement with these results, mutations of F22-E23, V25 and Y41, G42, N44, L45 on ECD1 abolished the binding of anti-Fy6 and anti-Fya mAbs to K562 cells respectively, Anti-Fy3 binding was abolished by D58-D59 (ECD1), R124 (ECD2), D263 and D283 (ECD4) substitutions. Mutations of C51 (ECD1), C129 (ECD2), C195 (ECD3) and C276 (ECD4 severely reduced anti-Fy3 and CXC-chemokine ligand 8 (CXCL-8) binding. CXCL-8 binding was also abrogated by mutations of F22-E23, P50 (ECD1) and D263, R267, D283 (ECD4). These results defined the Fya epitope and suggested that (1) two disulphide bridges are involved in the creation of an active chemokine binding pocket; (2) a limited number of amino acids in ECDs 1-4 participate in CXCL-8 binding; and (3) Fy3 is a conformation-dependent epitope involving all ECDs. We also showed that N-glycosylation of DARC occurred on N16SS and did not influence antibody and chemokine binding.