Anti-JC virus antibodies in a large German natalizumab-treated multiple sclerosis cohort.

OBJECTIVE: To investigate the rate of seropositivity of anti-JC virus (JCV) antibodies in a German multiple sclerosis (MS) cohort treated with natalizumab in the postmarketing setting and to assess anti-JCV serostatus in samples obtained before diagnosis of progressive multifocal leukoencephalopathy (PML). METHODS: This was a blinded, retrospective cross-sectional and longitudinal analysis for anti-JCV antibodies using a confirmatory 2-step ELISA on 2,782 blood samples obtained from 2,253 patients nationwide for routine testing for anti-natalizumab antibodies during open-label treatment between 2007 and 2010. RESULTS: Of the natalizumab-treated patients with MS, 58.8% tested positive for anti-JCV antibodies. The rate of seropositivity was higher in males and increased with age, with a plateau between age intervals 20-29 and 30-39 years. In longitudinal analyses, 19 of 194 (9.8%) patients converted from anti-JCV antibody-negative to seropositive status over 7.7 months; 4.7% reverted from antibody-positive to seronegative status over 7.9 months. Antibody levels, especially in the latter group, were low, indicating fluctuations around the lower cut point of the assay. Neither anti-JCV serostatus nor antibody levels were associated with immunosuppressive pretreatment, duration of natalizumab treatment, or anti-natalizumab antibodies. All samples obtained from 10 patients who developed PML were seropositive (13 samples before PML diagnosis [2.0-37.6 months]; 2 samples at diagnosis). Antibody levels in these samples were higher than those in samples from seropositive patients who did not develop PML. CONCLUSIONS: These data argue for the potential clinical utility of JCV serology for PML risk stratification. However, further investigations of fluctuations in serostatus and of antibody levels for a more precise understanding of the predictive value are warranted.

Proof of concept studies for tissue-protective agents in multiple sclerosis.

BACKGROUND: There is considerable interest in tissue-protective treatments for multiple sclerosis (MS). METHODS AND OBJECTIVES: We convened a group of MS clinical trialists and related researchers to discuss designs for proof of concept studies utilizing currently available data and assessment methods. RESULTS: Our favored design was a randomized, double-blind, parallel-group study of active treatment versus placebo focusing on changes in brain volume from a post-baseline scan (3-6 months after starting treatment) to the final visit 1 year later. Study designs aimed at reducing residual deficits following acute exacerbations are less straightforward, depending greatly on the anticipated rapidity of treatment effect onset. CONCLUSIONS: The next step would be to perform one or more studies of potential tissue-protective agents with these designs in mind, creating the longitudinal data necessary to refine endpoint selection, eligibility criteria, and sample size estimates for future trials.

Effect of plasma exchange in accelerating natalizumab clearance and restoring leukocyte function.

BACKGROUND: Accelerating the clearance of therapeutic monoclonal antibodies (mAbs) from the body may be useful to address uncommon but serious complications from treatment, such as progressive multifocal leukoencephalopathy (PML). Treatment of PML requires immune reconstitution. Plasma exchange (PLEX) may accelerate mAb clearance, restoring the function of inhibited proteins and increasing the number or function of leukocytes entering the CNS. We evaluated the efficacy of PLEX in accelerating natalizumab (a therapy for multiple sclerosis [MS] and Crohn disease) clearance and alpha4-integrin desaturation. Restoration of leukocyte transmigratory capacity was evaluated using an in vitro blood-brain barrier (ivBBB). METHODS: Twelve patients with MS receiving natalizumab underwent three 1.5-volume PLEX sessions over 5 or 8 days. Natalizumab concentrations and alpha4-integrin saturation were assessed daily throughout PLEX and three times over the subsequent 2 weeks, comparing results with the same patients the previous month. Peripheral blood mononuclear cell (PBMC) migration (induced by the chemokine CCL2) across an ivBBB was assessed in a subset of six patients with and without PLEX. RESULTS: Serum natalizumab concentrations were reduced by a mean of 92% from baseline to 1 week after three PLEX sessions (p < 0.001). Although average alpha4-integrin saturation was not reduced after PLEX, it was reduced to less than 50% when natalizumab concentrations were below 1 mug/mL. PBMC transmigratory capacity increased 2.2-fold after PLEX (p < 0.006). CONCLUSIONS: Plasma exchange (PLEX) accelerated clearance of natalizumab, and at natalizumab concentrations below 1 mug/mL, desaturation of alpha4-integrin was observed. Also, CCL2-induced leukocyte transmigration across an in vitro blood-brain barrier was increased after PLEX. Therefore, PLEX may be effective in restoring immune effector function in natalizumab-treated patients.

Fumaric acid esters are effective in chronic experimental autoimmune encephalomyelitis and suppress macrophage infiltration.

Fumaric acid esters (FAE) have proven their therapeutic efficacy in psoriasis, a Th1 mediated skin disease. More recently, preliminary data have suggested an activity in multiple sclerosis (MS) as well. To investigate further possible mechanisms of action of these compounds in inflammatory diseases, we studied the FAE methyl hydrogen fumarate (MHF) and dimethyl fumarate (DMF) in chronic experimental autoimmune encephalomyelitis (EAE) induced by immunization of C57BL/6 mice with MOG peptide aa 35-55. Preventive treatment with these FAE was delivered twice a day by oral gavage. Both esters had a significant therapeutic effect on the disease course and histology showed a strongly reduced macrophage inflammation in the spinal cord. Multiparameter cytokine analysis from blood detected an increase of IL-10 in the treated animals. We conclude that the underlying biological activity of FAE in EAE is complex and, to elucidate the molecular mechanisms, further investigation is needed.

Neutralizing antibodies and efficacy of interferon beta-1a: a 4-year controlled study.

OBJECTIVE: To determine the incidence and clinical significance of neutralizing antibody (NAb) formation in patients with relapsing multiple sclerosis (MS) who participated in the European Interferon Beta-1a IM Dose-Comparison Study. METHODS: Patients were randomized to treatment with interferon beta-1a (IFNbeta-1a) 30 microg or 60 microg IM once weekly for up to 4 years. Serum samples obtained at baseline and every 3 months thereafter were screened for the presence of IFN binding antibodies by ELISA. Patients whose results were seropositive on ELISA were screened for the presence of NAbs using an antiviral cytopathic effect assay. Patients were considered to be positive for NAbs (NAb+) if the baseline NAb titer was 0 and two or more consecutive postbaseline titers were > or = 20. Patients were considered to be negative for NAbs (NAb-) if the baseline NAb titer was 0 and all postbaseline NAb titers were < 5. RESULTS: The proportion of patients who became NAb+ was lower in patients who received 30 microg of IFNbeta-1a than in those who received 60 microg (7/400 [1.8%] vs 19/395 [4.8%]; p = 0.02). The mean time to NAb+ status was 14.5 +/- 6.2 months. Compared with patients who remained NAb-, NAb+ patients showed the following: higher relapse rates from months 12 to 48 (p = 0.04), higher rate of mean change (worsening) in Expanded Disability Status Scale score from baseline to month 48 (p = 0.01), greater number of T1 gadolinium-enhanced lesions at months 24 and 36 (p = 0.02 and 0.03), and greater accrual of new or enlarging T2 lesions from month 12 to months 24 and 36 (p = 0.05 and 0.09). CONCLUSIONS: Neutralizing antibodies (NAbs) to interferon beta-1a (IFNbeta-1a), as observed with other IFNbetas used in the treatment of multiple sclerosis, reduce the therapeutic benefits measured by relapses and MRI activity. Data from this study also suggest NAbs to IFNbeta-1a reduce treatment benefits as measured by change in Expanded Disability Status Scale score.

Analysis of the performance of the Hartmann-Shack sensor in the human eye.

A description of a Hartmann-Shack sensor to measure the aberrations of the human eye is presented. We performed an analysis of the accuracy and limitations of the sensor using experimental results and computer simulations. We compared the ocular modulation transfer function obtained from simultaneously recorded double-pass and Hartmann-Shack images. The following factors affecting the sensor performance were evaluated: the statistical accuracy, the number of modes used to reconstruct the wave front, the size of the microlenses, and the exposure time.

Differences in activity between alpha and beta type I interferons explored by mutational analysis.

Type I interferon (IFN) subtypes alpha and beta share a common multicomponent, cell surface receptor and elicit a similar range of biological responses, including antiviral, antiproliferative, and immunomodulatory activities. However, alpha and beta IFNs exhibit key differences in several biological properties. For example, IFN-beta, but not IFN-alpha, induces the association of tyrosine-phosphorylated receptor components ifnar1 and ifnar2, and has activity in cells lacking the IFN receptor-associated, Janus kinase tyk2. To define the structural basis for these functional differences we produced human IFN-beta with point mutations and compared them to wild-type IFN-beta in assays that distinguish alpha and beta IFN subtypes. IFN-beta mutants with charged residues (N86K, N86E, or Y92D) introduced at two positions in the C helix lost the ability to induce the association of tyrosine-phosphorylated receptor chains and had reduced activity on tyk2-deficient cells. The combination of negatively charged residues N86E and Y92D (homologous with IFN-alpha8) increased the cross-species activity of the mutant IFN-betas on bovine cells to a level comparable to that of human IFN-alphas. In contrast, point mutations in the AB loop and D helix had no significant effect on these subtype-specific activities. A subset of these latter mutations did, however, reduce activity in a manner analogous to IFN-alpha mutations. The effects of these mutations on IFN-beta activity are discussed in the context of a family of related ligands acting through a common receptor and signaling pathway.

Structural and functional differences between glycosylated and non-glycosylated forms of human interferon-beta (IFN-beta).

PURPOSE: Two recombinant IFN-beta products have been approved for the treatment of multiple sclerosis, a glycosylated form with the predicted natural amino acid sequence (IFN-beta-1a) and a non-glycosylated form that has a Met-1 deletion and a Cys-17 to Ser mutation (IFN-beta-1b). The structural basis for activity differences between IFN-beta-1a and IFN-beta-1b, is determined. METHODS: In vitro antiviral, antiproliferative and immunomodulatory assays were used to directly compare the two IFN-beta products. Size exclusion chromatography (SEC), SDS-PAGE, thermal denaturation, and X-ray crystallography were used to examine structural differences. RESULTS: IFN-beta-1a was 10 times more active than IFN-beta-1b with specific activities in a standard antiviral assay of 20 x 10(7) IU/mg for IFN-beta-1a and 2 x 10(7) IU/mg for IFN-beta-1b. Of the known structural differences between IFN-beta-1a and IFN-beta-1b, only glycosylation affected in vitro activity. Deglycosylation of IFN-beta-1a produced a decrease in total activity that was primarily caused by the formation of an insoluble disulfide-linked IFN precipitate. Deglycosylation also resulted in an increased sensitivity to thermal denaturation. SEC data for IFN-beta-1b revealed large, soluble aggregates that had reduced antiviral activity (approximated at 0.7 x 10(7) IU/mg). Crystallographic data for IFN-beta-1a revealed that the glycan formed H-bonds with the peptide backbone and shielded an uncharged surface from solvent exposure. CONCLUSIONS: Together these results suggest that the greater biological activity of IFN-beta-1a is due to a stabilizing effect of the carbohydrate on structure.

Inhibition of vascular smooth muscle cell proliferation and intimal hyperplasia by gene transfer of beta-interferon.

BACKGROUND: Balloon injury of the arterial wall induces increased vascular smooth cell proliferation, enhanced elastic recoil, and abnormalities in thrombosis, each of which contribute to regrowth of intima and the lesion of restenosis. Several gene transfer approaches have been used to inhibit such intimal smooth muscle cell growth. In this report, adenoviral gene transfer of beta-interferon (beta-IFN) was analyzed in a porcine model of balloon injury to determine whether a secreted growth inhibitory protein might affect the regrowth of vascular smooth muscle cells in vitro and in arteries. MATERIALS AND METHODS: An adenoviral vector encoding beta-interferon (ADV-beta-IFN) was prepared and used to infect porcine vascular smooth muscle cells in a porcine balloon injury model. Its antiproliferative effect was analyzed in vitro and in vivo. RESULTS: Expression of recombinant porcine beta-IFN in vascular smooth muscle cells reduced cell proliferation significantly in vitro, and supernatants derived from the beta-IFN vector inhibited vascular smooth muscle cell proliferation relative to controls. When introduced into porcine arteries after balloon injury, a reduction in cell proliferation was observed 7 days after gene transfer measured by BrdC incorporation (ADV-delta E1 arteries 14.5 +/- 1.2%, ADV-beta IFN 6.8 +/- 0.8%, p < 0.05, unpaired, two-tailed t-test). The intima-to-media area ratio was also reduced (nontransfected arteries, 0.70 +/- 0.05; ADV-delta E1 infected arteries, 0.69 +/- 0.06; ADV-beta-IFN infected arteries, 0.53 +/- 0.03; p < 0.05, ANOVA with Dunnett t-test). No evidence of organ toxicity was observed, and regrowth of the endothelial cell surface was observed 3-6 weeks after balloon injury. CONCLUSIONS: Gene transfer of an adenoviral vector encoding beta-IFN into balloon-injured arteries reduced vascular smooth muscle proliferation and intimal formation. Expression of this gene product may have potential application for the treatment of vascular proliferative diseases.

The crystal structure of human interferon beta at 2.2-A resolution.

Type I interferons (IFNs) are helical cytokines that have diverse biological activities despite the fact that they appear to interact with the same receptor system. To achieve a better understanding of the structural basis for the different activities of alpha and beta IFNs, we have determined the crystal structure of glycosylated human IFN-beta at 2.2-A resolution by molecular replacement. The molecule adopts a fold similar to that of the previously determined structures of murine IFN-beta and human IFN-alpha2b but displays several distinct structural features. Like human IFN-alpha2b, human IFN-beta contains a zinc-binding site at the interface of the two molecules in the asymmetric unit, raising the question of functional relevance for IFN-beta dimers. However, unlike the human IFN-alpha2b dimer, in which homologous surfaces form the interface, human IFN-beta dimerizes with contact surfaces from opposite sides of the molecule. The relevance of the structure to the effects of point mutations in IFN-beta at specific exposed residues is discussed. A potential role of ligand-ligand interactions in the conformational assembly of IFN receptor components is discussed.

Inhibition of alpha interferon but not gamma interferon signal transduction by phorbol esters is mediated by a tyrosine phosphatase.

Previous studies have indicated that the expression of viral oncoproteins, cell transformation, or phorbol ester treatment of cells can inhibit alpha/beta interferon (IFN-alpha/beta)-induced gene expression. The mechanisms by which these promoters of cell growth exert their inhibitory effects vary, but in most instances they involve a disruption of the IFN-alpha/beta-induced transcription complex ISGF3 such that the DNA-binding component of this complex (the 48-kDa ISGF3gamma protein) does not bind to the interferon-stimulated response element (ISRE). In this report, we demonstrated that phorbol ester treatment of human peripheral blood monocytes dramatically inhibits activation of IFN-alpha/B-stimulated early response genes but by a mechanism which does not involve abrogation of the ISRE binding of ISGF3gamma. Phorbol ester treatment of monocytes inhibited IFN alpha-stimulated tyrosine phosphorylation of the transcription factors Stat1alpha, Stat2, and Stat3 and of the tyrosine kinase Tyk2 but had no effect on IFN-gamma activation of Stat1alpha. IFNalpha-stimulated tyrosine phosphorylation of Jak1 and the alpha subunit of the IFN-alpha receptor were unaffected by phorbol 12-myristate 13-acetate (PMA). Moreover, PMA caused the dephosphorylation of Tyk2 but not of Jak1, which was activated by IFN. Pretreatment of cells with vanadate prevented the effects of PMA with regard to PMA-induced Tyk2 dephosphorylation. These observations suggest that PMA exerts its inhibitory effects by activation of a tyrosine phosphatase which selectively regulates Tyk2 but not Jak1 activity.

Differential regulation of the alpha/beta interferon-stimulated Jak/Stat pathway by the SH2 domain-containing tyrosine phosphatase SHPTP1.

Interferons (IFNs) induce early-response genes by stimulating Janus family (Jak) tyrosine kinases, leading to tyrosine phosphorylation of Stat transcription factors. Previous studies implicated protein-tyrosine phosphatase (PTP) activity in the control of IFN-regulated Jak/Stat signaling, but the specific PTPs responsible remained unidentified. We have found that SH2 domain-containing PTP1 (SHPTP1; also called PTP1C, HCP, or SHP) reversibly associates with the IFN-alpha receptor complex upon IFN addition. Compared with macrophages from normal littermate controls, macrophages from motheaten mice, which lack SHPTP1, show dramatically increased Jak1 and Stat1 alpha tyrosine phosphorylation, whereas Tyk2 and Stat2 activation is largely unaffected. These findings correlate with selectively increased complex formation on a gamma response element, but not an IFN-stimulated response element, in motheaten macrophages. Our results establish that SHPTP1 selectively regulates distinct components of Jak/Stat signal transduction pathways in vivo.

Configuration of the interferon-alpha/beta receptor complex determines the context of the biological response.

Constituents of the Type 1 interferon (IFN) receptor (IFNABR) identified to date include the alpha and beta transmembrane subunits and the associated intracellular kinases, Jak 1 and Tyk 2. In this report, we demonstrate that a human cell type that expresses both subunits of IFNABR, together with Jak 1 and Tyk 2, exhibits a limited binding capacity for and is only partially sensitive to the effects of IFN-alpha/beta, despite adequate levels of the cytoplasmic transcription factors Stat1, Stat2, and Stat3. Specifically, a low affinity interaction between IFN-alpha/beta and cell surface receptors results in ISGF3 (Stat1:2) activation and an antiviral response, yet no IFN-inducible growth inhibition. Using a panel of murine cells that are variably configured with respect to the human IFNABR-alpha/beta subunits, we provide evidence that an additional component(s) encoded on human chromosome 21 is required to confer high affinity binding and IFN-inducible growth inhibition to cells that express the alpha and beta subunits of the IFNABR. The data indicate that transcriptional activation that leads to an antiviral response is mediated by IFN-alpha/beta activation of IFNABR-alpha and IFNABR-beta in the context of a low affinity interaction, yet a high affinity interaction is necessary for signal transducing events that mediate growth inhibition. We provide evidence that the extent of ISGF3 activation correlates directly with the magnitude of an antiviral but not a growth inhibitory response.

Identification of endogenous protein-associated carbohydrate ligands for E-selectin.

A comparative analysis of carbohydrate libraries derived from cell lines binding E-selectin was used to identify endogenous protein-associated carbohydrate ligands for E-selectin. Three structures, which together constitute less than 1% of the total cell surface protein-associated carbohydrate, were unique to cell lines capable of binding E-selectin, including neutrophils and the monocytic cell line U937. All are tetra-antennary N-linked structures, with a sialic acid alpha 2 --> 3 galactose beta 1 --> 4 (fucose alpha 1 --> 3) N-acetyl glucosamine beta 1 --> 3 galactose beta 1 --> 4 (fucose alpha 1 --> 3) N-acetyl glucosamine lactosaminoglycan extension (sialyl-di-Lewis X [S-diLe(x)]) on the arm linked through the C4 residue on the mannose. While all contained the expected 3-SLe(x) sub-structure, these native structures have an additional fucosylated lactosamine unit. Direct evidence that these S-di-Lex-containing structures are high-affinity ligands for E-selectin came from the use of recombinant soluble E-selectin-agarose affinity chromatography. These three carbohydrate structures bound specifically to the E-selectin column, while 3-SLe(x) itself does not bind under identical conditions.

Human type I interferon receptor, IFNAR, is a heavily glycosylated 120-130 kD membrane protein.

Type I interferons (IFNs) bind and signal through cell surface receptors that share at least one common component. One candidate for such a component is the interferon-alpha receptor (IFNAR). Genetic studies have shown that the IFNAR gene product is required for response to many type I interferons. However, these studies also suggest that the IFNAR protein interacts with an additional receptor component(s) to form functionally complete type I IFN receptors. Although these genetic studies have contributed significantly to understanding the type I IFN receptors. Although these genetic studies have contributed significantly to understanding the type I IFN receptors, little biochemical characterization of IFNAR and its function has been reported. To facilitate biochemical studies of the IFNAR gene product, a monoclonal antibody, GB8, recognizing the extracellular domain of IFNAR was prepared. The epitope for GB8 maps to the second extracellular domain of IFNAR between amino acids 278 and 293. GB8 identifies IFNAR in western blots of cell membranes as a broad band with molecular mass ranging from 100 to 150 kD in membranes from CHO cells overexpressing the human IFNAR gene to 136-150 kD in Daudi cell membranes. Such variations in the mean value and the range of molecular mass between IFNAR in different cell lines suggest differences in glycosylation. The majority of glycosylation is N-linked, although there may also be a small amount O-linked oligosaccharide. Deglycosylation of IFNAR in Daudi cell membranes results in a 70 kD IFNAR species, indicating that nearly half of the apparent molecular mass of Daudi cell IFNAR is contributed by carbohydrate moieties.

Isolation and characterization of natural protein-associated carbohydrate ligands for E-selectin.

A comparative analysis of carbohydrate 'libraries' derived from cell lines binding E-selectin with differing avidity identified endogenous protein-associated carbohydrate ligand candidates for E-selectin. Three unusual structures, which constitute less than 3% of cell surface protein-associated carbohydrate, were unique to the E-selectin-binding cells, including neutrophils and the monocytic cell line U937. All are tetraantennary N-linked structures with a NeuAc alpha 2-->3Gal beta 1-->4(Fuc alpha 1-->3)GlcNAc beta 1-->3Gal beta 1-->4- (Fuc alpha 1-->3)GlcNAc lactosaminoglycan extension (diSLex) on the arm linked through the C4 residue on the mannose. While all contained the expected SLex [NeuAc alpha 2-->3Gal beta 1-->4(Fuc alpha 1-->3)GlcNAc] moiety, these structures have an additional fucosylated lactosamine unit. Direct evidence that these diSLex-containing structures are, indeed, high-affinity ligands for E-selectin came from the use of recombinant soluble E-selectin-agarose affinity chromatography. We found that these three carbohydrate structures bound specifically to the E-selectin column. SLex itself does not bind under identical conditions. In summary, these related structures: (1) all possess an unusual 3-sialyl di-Lewis x extension on one arm of an N-linked tetraantennary glycan; (2) of the cells tested, are present only on E-selectin-binding leukocytes and leukocytic cell lines; (3) bind to E-selectin with a relatively high affinity (Kd < microM) and one greater than that of 3-sialyl Lewis x or 3-sialyl Lewis a; and (4) represent a very small percentage of the protein-associated carbohydrate. These carbohydrate structures appear to be present on only a very small number of cell surface proteins and may alone be responsible for the specificity of E-selectin-dependent adhesion.

Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor.

A Hartmann-Shack wave-front sensor is used to measure the wave aberrations of the human eye by sensing the wave front emerging from the eye produced by the retinal reflection of a focused light spot on the fovea. Since the test involves the measurements of the local slopes of the wave front, the actual wave front is reconstructed by the use of wave-front estimation with Zernike polynomials. From the estimated Zernike coefficients of the tested wave front the aberrations of the eye are evaluated. It is shown that with this method, using a Hartmann-Shack wave-front sensor, one can obtain a fast, precise, and objective measurement of the aberrations of the eye.

Differential expression of an E-selectin ligand (SLex) by two Chinese hamster ovary cell lines transfected with the same alpha (1,3)-fucosyltransferase gene (ELFT).

The mammalian cDNA encoding alpha (1,3)-fucosyltransferase (alpha (1,3)Fuc-T) termed ELAM-1 ligand fucosyltransferase (ELFT) or Fuc-TIV was previously cloned by three groups who reported different results from transfection studies Goelz et al. (Goelz, S. E., Hession, C., Goff, D., Griffiths, B., Tizard, R., Newman, B., Chi-Rosso, G., and Lobb, R. (1990) Cell 63, 1349-1356) found that Chinese hamster ovary (CHO) cells expressing the ELFT cDNA had alpha (1,3)Fuc-T activity and were able to bind to E-selectin. In contrast, Lowe et al. (Lowe, J. B., Kukowska-Latallo, J. F., Nair, R. P., Larsen, R. D., Marks, R. M., Macher, B. A., Kelly, R. J., and Ernst, L. K. (1991) J. Biol. Chem. 266, 17467-17477) and Kumar et al. (Kumar, R., Potvin, B., Muller, W. A., and Stanley, P. (1991) J. Biol. Chem. 266, 21777-21783) found no binding to E-selectin of CHO transfectants expressing the same alpha (1,3)Fuc-T gene; nor did the latter transfectants synthesize a known E-selectin ligand, sialylated Lex (SLex), although they had substantial alpha (1,3)Fuc-T activity. We now show that these discrepant results were due to a difference between the parental CHO cell lines. Following transfection of ELFT cDNA into Pro-5 or dihydrofolate reductase (DHFR)- CHO cells, only the DHFR- transfectants expressed SLex and bound to E-selectin. Indirect evidence from monoclonal antibody and lectin binding studies indicates that the range of carbohydrate structures synthesized by the Pro-5 and DHFR- CHO cell lines differs. Since DHFR-/ELFT transfectants expressed cell surface SLex but transferred fucose poorly to sialylated substrates in vitro, ELFT may be able to fucosylate a complex carbohydrate missing from Pro-5 cells. Alternatively, either CHO line may have an activity (such as an alpha (2,3)-sialyltransferase), that modifies alpha (1,3)-fucosylated lactosamines.

The ELAM ligand fucosyltransferase, ELFT, directs E-selectin binding to a secreted scaffold protein: a method to produce and purify large quantities of specific carbohydrate structures.

Many biological processes depend on cell surface recognition of receptor-ligand pairs. Some receptors, such as the selectins, recognize specific carbohydrate structures as part of their ligands. The ability to synthesize such ligands for use in the study of cell adhesion mechanisms or as inhibitors of a variety of pathological conditions would be extremely useful. However, the chemical or enzymic in vitro synthesis of carbohydrate-based ligands has thus far been difficult and costly. We have used E-selectin and its carbohydrate ligand as a model system to test if it is possible to express specific carbohydrate structures on a secreted, glycosylated and easily purified scaffold protein and to use this newly modified protein as a functional adhesion molecule. We co-expressed a fucosyltransferase (ELFT) and a secreted immunoglobulin-LFA3 fusion protein (LFA31G) in the same cell to modify the carbohydrate structures on the secreted LFA3IG scaffold protein (we refer to this novel protein as X-LFA3IG). Using glycosidase digestion, lectin binding, carbohydrate composition analysis and antibody-binding assays, we show that approximately 50% of the potential N-linked carbohydrate sites on X-LFA3IG are, indeed, modified and that the modification is the addition of fucose. Furthermore, we show that X-LFA3IG contains epitopes recognized by anti-Slex antibodies, and, using an E-selectin-specific adhesion assay, we demonstrate that X-LFA3IG is a functional ligand for E-selectin. This in vivo approach for generating specific carbohydrate structures could be generalized to produce and purify large quantities of other biologically important carbohydrate structures.