Apparent dispensability of the carbohydrate moiety of human interferon for antiviral activity.

Human leukocyte and tritium-labeled fibroblast interferons, prepared by induction with Sendai virus and with double-stranded polyinosinic acid.polycytidylic acid respectively, have been studied in relation to the carbohydrate moieties attached to them. These interferons were partially purified by immunoabsorbance and by gel filtration. On treatment with glycosidases, about 80% of the 3H-labeled sugar moieties in this glycoprotein-containing fraction was removed without detectable alteration of the antiviral activity or antibody-binding properties characteristic of interferon. The molecular weight of leukocyte interferon was reduced by about 4000. As others have reported, the heterogeneous character of interferon revealed by isoelectric focusing was greatly reduced by the enzyme treatment.     

Antiviral and protein-inducing activities of recombinant human leukocyte interferons and their hybrids.

The antiviral activities of recombinant human leukocyte interferons IFN-alpha A and IFN-alpha D as well as five hybrids of these interferons against retroviruses, vesicular stomatitis virus, and encephalomyocarditis virus were studied in feline, human, and murine cells. Although these interferon species had widely different potencies, their activities against these viruses were, in general, proportional. The IFN-alpha A/D (Bgl) hybrid was the most potent species, and the IFN-alpha D/A (Bgl) hybrid was the least potent. However, the latter species did not interfere with the action of the former species. Like natural human leukocyte interferon, each of the seven species of recombinant interferons induced the synthesis of at least five proteins in human fibroblasts, whereas induction of only one such protein was readily detected in a feline fibroblast line in which these interferon species inhibited the replication of all three viruses.     

Isolation and characterization of the receptor on human neutrophils that mediates cellular adherence

The receptor on human neutrophils (polymorphonuclear leukocytes or PMN) that mediates cellular adherence has been purified from the peripheral blood PMN obtained from an individual with chronic myelogenous leukemia (CML). This receptor consists of two noncovalently associated subunits, designated alpha M (Mac-1 alpha, CD11b) (Mr = 170,000) and beta (Mac-1 beta, CDw18) (Mr = 100,000), respectively, which are identical on normal and CML PMN. The subunits were purified by monoclonal antibody 60.1-Sepharose (anti-alpha M) affinity chromatography and separated in 5-nmol quantities by high pressure liquid chromatography on a TSK-4000 gel filtration column. Subunits were characterized by amino acid composition, NH2-terminal amino acid sequence, and carbohydrate content. The NH2-terminal sequence of the human PMN alpha M subunit contains regions of homology with the human platelet glycoprotein IIb alpha. We conclude that nanomole amounts of individual alpha M and beta subunits of the receptor on human PMN that mediates cellular adherence can be isolated and separated using CML PMN.     

Hybrid recombinant human leukocyte interferon inhibits differentiation in murine B-16 melanoma cells

We have investigated the effects of recombinant human leukocyte interferons (IFN-alpha A and IFN-alpha D) and various hybrid recombinant human leukocyte interferons on differentiation in B-16 mouse melanoma cells. Inhibition of both spontaneous and melanocyte hormone stimulated differentiation was observed with one hybrid construct, IFN-alpha A/D (Bgl) consisting of amino acids 1 to 62 from IFN-alpha A and amino acids 64 to 166 from IFN-alpha D. In contrast, the parental human interferons, IFN-alpha A and IFN-alpha D, when used alone or in combination, as well as other hybrid human leukocyte interferons, did not cause significant inhibition of melanogenesis in B-16 mouse cells. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) also inhibited B-16 differentiation and the combination of TPA with IFN-alpha A/D (Bgl) or mouse L-cell interferon was synergistic in delaying melanogenesis. These studies indicate that the IFN-alpha A/D (Bgl) hybrid that exhibits antiviral activity on mouse cells can also inhibit differentiation of murine cells.     

Expression of interferon consensus sequence binding protein (ICSBP) is downregulated in Bcr-Abl-induced murine chronic myelogenous leukemia-like disease, and forced coexpression of ICSBP inhibits Bcr-Abl-induced myeloproliferative disorder

Chronic myelogenous leukemia (CML) is a clonal myeloproliferative disorder resulting from the neoplastic transformation of a hematopoietic stem cell. The majority of cases of CML are associated with the (9;22) chromosome translocation that generates the bcr-abl chimeric gene. Alpha interferon (IFN-alpha) treatment induces hematological remission and prolongs life in 75% of CML patients in the chronic phase. It has been shown that mice deficient in interferon consensus sequence binding protein (ICSBP), a member of the interferon regulatory factor family, manifest a CML-like syndrome. We have shown that expression of Bcr-Abl in bone marrow (BM) cells from 5-fluorouracil (5-FU)-treated mice by retroviral transduction efficiently induces a myeloproliferative disease in mice resembling human CML. To directly test whether icsbp can function as a tumor suppressor gene, we examined the effect of ICSBP on Bcr-Abl-induced CML-like disease using this murine model for CML. We found that expression of the ICSBP protein was significantly decreased in Bcr-Abl-induced CML-like disease. Forced coexpression of ICSBP inhibited the Bcr-Abl-induced colony formation of BM cells from 5-FU-treated mice in vitro and Bcr-Abl-induced CML-like disease in vivo. Interestingly, coexpression of ICSBP and Bcr-Abl induced a transient B-lymphoproliferative disorder in the murine model of Bcr-Abl-induced CML-like disease. Overexpression of ICSBP consistently promotes rather than inhibits Bcr-Abl-induced B lymphoproliferation in a murine model where BM cells from non-5-FU-treated donors were used, indicating that ICSBP has a specific antitumor activity toward myeloid neoplasms. We also found that overexpression of ICSBP negatively regulated normal hematopoiesis. These data provide direct evidence that ICSBP can act as a tumor suppressor that regulates normal and neoplastic proliferation of hematopoietic cells.     

Structures of the carbohydrate chains of membrane glycoproteins IIb and IIIa of human platelets

Human platelet membrane glycoproteins IIb (GPIIb) and IIIa (GPIIIa), which have been proposed to be subunits of a receptor for fibrinogen, were purified from Triton X-100-solubilized platelet membranes by affinity chromatography on a concanavalin A (Con A)-Sepharose column followed by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Compositional analyses of the purified glycoproteins showed that GPIIb and GPIIIa contain 15% and 18% carbohydrate by weight, respectively, which consists of galactose, mannose, glucosamine, fucose, and sialic acid. This suggested that these glycoproteins contained N-linked carbohydrate chains. The carbohydrate chains were released from each glycoprotein by hydrazinolysis and then fractionated by ion-exchange chromatography on a Mono Q column. From each glycoprotein, mono-, di-, and trisialylated and neutral oligosaccharide fractions were obtained. The structures of these oligosaccharides were investigated by means of compositional and methylation analyses and digestion by exoglycosidase, and their reactivities to immobilized lectins were also examined. The neutral oligosaccharides, which comprised about 14% of the total oligosaccharides released from GPIIb and about 52% of that from GPIIIa, were found to be of the high mannose-type, in that they contained 5 or 6 mannose residues. On the other hand, a major part of the acidic oligosaccharides was found to consist of typical bi- and triantennary complex-type sugar chains, and much smaller amounts of tetraantennary complex-type sugar chains, and complex-type sugar chains with a fucosyl residue at a N-acetylglucosamine residue in the peripheral portion or a bisecting N-acetylglucosamine at a beta-mannosyl residue in the core portion were also detected. In conclusion, we found that GPIIb contained mainly complex-type sugar chains, whereas high mannose-type sugar chains were the predominant carbohydrate units in GPIIIa, and that the detected differences in the carbohydrate moieties of GPIIb and GPIIIa were quantitative but not qualitative.     

Immunochemical and biological properties of synthetic peptide fragments from the 124-144 sequence of human leukocyte interferon alpha2]

Three peptides corresponding to the sequences 124-144, 124-138, 129-144 of the human leukocyte interferon alpha 2 (IFN-alpha 2) were synthesized. The synthesis was performed by DCC-HOBT coupling of protected peptide segments in solution. The segments were obtained by the active ester coupling methodology using base-labile 2-[4-(phenylazobenzyl)sulfonyl]ethyl (Pse) group as carboxyterminal protection. After complete deprotection with 1 M methanesulphonic acid in trifluoroacetic acid--thioanisol--m-cresol mixture the peptides were purified by reversed-phase chromatography. The studies of interaction of the peptides with rabbit antiserum against IFN-alpha 2 revealed at least one minor antigenic determinant within the 124-144 region of IFN-alpha 2 amino acid sequence. Rabbit antisera developed against peptides 124-138 and 129-144 showed ability of binding recombinant IFN-alpha 2 and neutralizing its antiviral activity. Free peptides or their conjugates with bovine serum albumine did not display antiviral activity, neither could they inhibit the activity of IFN-alpha 2.     

Secondary structure of human leukocyte interferon from Raman spectroscopy

Raman spectra were taken of human alpha (leukocyte) interferon subtype A (HuIFN-alpha A) purified from extracts of transformed Escherichia coli. Quantitative analysis of the conformationally sensitive amide I band indicates that IFN (interferon)-alpha A is 75 +/- 5% helical and 7 +/- 4% beta-strand. An independent analysis of the amide III spectrum indicates 71 +/- 5% helix and 10 +/- 6% beta-strand. These results differ with a recently proposed three-dimensional model based on secondary structure predictions derived from sequence and with circular dichroism measurements. The Raman spectrum of IFN-alpha A is compared with the spectra of several other helical proteins: hemerythrin, intestinal calcium-binding protein, melittin, and insulin.     

Bacteria-derived human leukocyte interferons alter in vitro humoral and cellular immune responses

Cultures of gradient-purified human peripheral blood mononuclear cells (PBMC) have been employed to examine the effects of three bacteria-derived human leukocyte interferon subtypes on certain aspects of in vitro immune responses. The addition of highly purified IFN-alpha 1, -alpha 2, -alpha 2/alpha 1 to PMBC cultures stimulated with phytohemagglutinin (PHA) or pokeweed mitogen resulted in a significant suppression of the mitogenic response. This suppression required the presence of interferon in the cultures because pretreatment of cells and removal of interferon had no effect on their response to PHA. The presence of these interferons at 200 U/ml also caused a substantial reduction of human mixed-lymphocyte reactions (MLR) as measured by [3H]thymidine incorporation by responder cells. Interestingly, pretreatment of stimulator cells was sufficient for this reduction to occur whereas pretreatment of responder cells had no effect on their ability to respond to allogenic stimulation. In contrast to these suppressive effects, the three interferons enhanced human in vitro primary immune response to sheep red blood cells (SRBC). These data demonstrate that both purified interferon subtypes and genetic hybrids of human interferons produced by recombinant DNA technology have effects on in vitro immune responses.     

Antiviral activities of hybrids of two major human leukocyte interferons.

Four hybrid human leukocyte interferon (LeIF or IFN-alpha) genes have been constructed by in vitro recombination of LeIF-A (IFN-alpha 2) and LeIF-D (IFN-alpha 1) genes at common restriction endonuclease sites located within their coding regions. These hybrid genes have been expressed in E. coli under trp promoter control. The interferons produced [LeIF-AD (BglII), -AD (PvuII), -DA (BglII), -DA (PvuII)] have antiviral properties distinct from the parental molecules LeIF-A and -D, varying considerably in their abilities to inhibit plaque formation by different viruses in a range of mammalian cells. All six of the cloned LeIFs exhibit the heat stability, pH 2 stability and antigenic specificity of natural leukocyte interferons.     

Enzymatic modifications of human fibroblast and leukocyte interferons

The sensitivity of highly purified human fibroblast interferon and partially purified human leukocyte interferon to several proteolytic and glycolytic enzymes was determined with respect to antiviral activity, isoelectric point, molecular weight, and thermal stability. Leucine aminopeptidase altered the distribution of isoelectric points for both interferons but produced little change in molecular weights; this enzyme somewhat reduced the activity of only leukocyte interferon. Treatment of fibroblast interferon with carboxypeptidases A and B did not greatly decrease antiviral activity, but it did slightly reduce the molecular weight of the interferon and substantially altered the distribution of isoelectric point values; similar treatment of leukocyte interferon caused some loss in activity, especially of the 17,000-molecular-weight species. Both interferons were inactivated rapidly by treatment with the endoproteases trypsin, pepsin, bromelain, and subtilisin. Chymotrypsin shifted the isoelectric points of both interferons, but only leukocyte interferon was significantly inactivated. Treatment with neuraminidase and beta-galactosidase changed the isoelectric point distribution but did not affect the activity or thermal stability of either interferon; such a treatment reduced the molecular weight of fibroblast interferon and the size heterogeneity of leukocyte interferon. Treatment with neuraminidase and then leucine aminopeptidase greatly reduced the activity of both interferons, especially leukocyte interferon. The data indicate that biologically active forms of fibroblast and leukocyte interferons can be distinguished by their relative sensitivity to certain proteases.     

Purification and characterization of interferons from a continuous myeloblastic cell line

Several leukocyte interferon species have been purified from a continuous human myeloblast cell line. The purification procedure involving selective precipitations, gel chromatography, and several steps of high performance liquid chromatography results in interferons with specific activities of 1 to 4 X 10(8) units/mg on bovine MDBK cells. The total yield of interferon is 23%, with the yield of the individual fractions ranging from 0.2 to 11.4%. Five fractions are homogeneous as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Molecular weights of the interferons were estimated by mobility on the sodium dodecyl sulfate gels and range from 17,600 to 26,200. The species differ in their relative antiviral activities on two cell lines, bovine MDBK and human AG-1732. In addition, the pure species have similar, but distinct, amino acid compositions and tryptic peptide profiles. These result support the conclusion that leukocyte interferon consists of several homologous proteins.     

Carbohydrates and carbohydrate esters of ferulic acid released from cell walls of Lolium multiflorum by treatment with cellulolytic enzymes

41% of the cell walls from mature leaf blades of Lolium multiflorum were digested by treatment during 14 days with C₁ enzyme (cellulase) which had been purified by gel filtration and ion-exchange chromatography. Cellobiose was the main sugar released from the walls, together with some glucose and higher oligosaccharides. Considerable amounts of carbohydrate esters of ferulic and p-coumaric acids were also released. When the C₁ enzyme was further purified by isoelectric focusing, only 8% of the cell walls were digested. Purified C_x (CM-cellulase) containing β-glucosidase digested 51% of the cell walls in 16 hours: the major component detected in the soluble products was glucose together with some β (1 → 4)-xylobiose, xylose and arabinose. Higher oligosaccharides and carbohydrate esters of ferulic and p-coumaric acids were also present. It was shown that these acids were present in the cell walls mainly in the trans-configuration.     

Hexoses as phloem transport sugars: the end of a dogma?

According to most textbooks, only non-reducing carbohydrate species such as sucrose, sugar alcohols, and raffinose-family sugars function as phloem translocates. Occasional abundance of reducing sugar species (such as hexoses) in sieve-tube sap has been discarded as an experimental artefact. This study, however, discloses a widespread occurrence of hexoses in the sieve-tube sap. Phloem exudation facilitated by EDTA provided evidence that many of the members of two plant families (Ranunculaceae and Papaveraceae) investigated translocate >80% of carbohydrates in the form of hexoses. Representatives of other families also appear to translocate appreciable amounts of hexoses in the sieve tubes. Promoting effects of EDTA, activities of sucrose-degrading enzymes, and sugar uptake by micro-organisms on hexose contents of phloem exudates were checked. The rate of sucrose degradation is far too low to explain the large proportions of hexoses measured in phloem exudates; nor did other factors tested seem to stimulate the occurrence of hexoses. The validity of the approach is further supported by the virtual absence of hexoses in exudates from species that were known as exclusive sucrose transporters. This study urges a rethink of the existing views on carbohydrate transport species in the phloem stream. Hexose translocation is to be regarded as a normal mode of carbohydrate transfer by the phloem equivalent to that of sucrose, raffinose-family sugars, or sugar alcohols.     

Purification and characterization of natural human interferon omega 1. Two alternative cleavage sites for the signal peptidase.

Human interferon omega 1 (IFN-omega 1 = IFN-alpha II1) is a recently discovered protein structurally related to IFN-alpha and -beta; the biological activities of IFN-omega 1 and its physiological role are not known to date. We have purified IFN-omega 1 from preparations of human leukocyte IFN, derived from peripheral blood leukocytes induced with Sendai virus, by two sequential cycles of monoclonal antibody affinity chromatography. The resulting protein was at least 95% pure as determined by reverse-phase high performance liquid chromatography and showed an Mr of 24,500 upon sodium dodecyl sulfate-gel electrophoresis (theoretical Mr, 19,984). Amino acid sequence analysis revealed that only about 40% of the molecules have the NH2 terminus expected on the basis of the sequence similarity to IFN-alpha, whereas the others contain two additional amino acids. This difference probably results from variable cleavage of the pre-protein by the signal peptidase. No evidence for COOH-terminal heterogeneity was found. Essentially all IFN-omega 1 molecules are glycosylated; enzymatic deglycosylation resulted in a reduction of the Mr to 20,500. Experiments using several plant lectins indicated the presence of biantennary complex oligosaccharides containing neuraminic acid. Two major peaks were observed upon chromatofocusing, with isoelectric points of 8.1 and 8.5. The specific antiviral activity of purified IFN-omega 1 assayed on human cells was determined to be 2.7 x 10(8) IU/mg, similar to that of other human class I IFNs; potent antiviral activity was also observed on cells of bovine and ovine but not of equine or murine origin.     

Roles of the 29-138 disulfide bond of subtype A of human alpha interferon in its antiviral activity and conformational stability

Human alpha (leukocyte) interferons contain two disulfide bonds between Cys-1 and Cys-98 and between Cys-29 and Cys-138. Reduction of interferon under native conditions leads to irreversible loss of antiviral activity; reduction in denaturant, followed by oxidation in native conditions, leads to restoration of activity. This behavior, unusual for disulfide-containing proteins, was studied by using a thiosulfonate derivative of subtype A of human alpha interferon (IFN-alpha A). The disulfide-free thiosulfonate formed at 25 degrees C has essentially no antiviral activity, while maintaining a conformation related to that of native IFN-alpha A. This species can regain activity after regeneration of its 29-138 disulfide, by thiol-disulfide interchange in native buffer. Incubation of the disulfide-free thiosulfonate under nonreducing conditions at 37 degrees C generates a monomeric species that has lost its native conformation as well as its ability to regain antiviral activity after thiol-disulfide interchange. These results explain the difficulty in obtaining, under native conditions, a reduced species that regains activity upon oxidation; complete reduction of IFN-alpha A in 100 mM 2-mercaptoethanol requires 37 degrees C, a temperature that promotes conformational decay of the disulfide-free form.     

Purification and chemical characterization of human platelet membrane glycoprotein IV

Human platelet membrane glycoprotein IV (GPIV), one of the major glycoprotein components, was purified by successive affinity chromatographies on columns of Lens culinaris agglutinin-Sepharose and wheat germ agglutinin-Sepharose followed by preparative polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). On SDS-polyacrylamide gel electrophoresis in either the presence or absence of dithiothreitol, GPIV gave a single band with an apparent molecular weight of 97,000, suggesting that GPIV is composed of a single polypeptide chain without interchain disulfide bonds. Compositional analysis showed that GPIV contains large amounts of acidic and hydroxy amino acids, but only very small amounts of cystine and methionine, and 28.1% (w/w) carbohydrate consisting of galactose, glucosamine, and sialic acid as the principal sugars with smaller amounts of fucose, mannose, and galactosamine. This suggested that GPIV contains both N-linked and O-linked sugar chains. The O-linked sugar chains isolated from GPIV, together with those from GPIb and glycocalicin, were comparatively analyzed on a Bio-Gel P-4 column after neuraminidase treatment. The results indicated that all three glycoproteins have two common species of carbohydrate chains, a disaccharide, Gal-GalNAc, and a tetrasaccharide, Gal-GlcNAc-(Gal-)GalNAc. The ratio of the tetrasaccharide to the disaccharide in GPIV was found to be somewhat different from that in GPIb or glycocalicin.     

Purification and characterization of a bovine pregnancy-associated glycoprotein

A 67000 Mr bovine pregnancy-associated glycoprotein (bPAG) has been isolated from fetal cotyledons and purified to homogeneity by HPLC. The purification was monitored by a double immunodiffusion test and by RIA in conjunction with an antiserum raised against a crude fraction of placenta-specific antigens. The molecular weight of bPAG was estimated to be 67000 by SDS-PAGE. The isoelectric points (pI) of the four isoforms, determined by high-resolution analytical electrofocusing in polyacrylamide gel, were 4.4, 4.6, 5.2, and 5.4. The carbohydrate content of the bPAG consisted of approximately 10.02 +/- 1.09% neutral sugar and variant amounts of sialic acid (from 0.29 +/- 0.06% in the most basic isoform to 2.1 +/- 0.31% in the most acidic isoform). A specific antiserum was raised against the purified bPAG. A specific RIA showed that the bPAG was antigenically unrelated to BSA, alphafetoprotein (AFP), and human schwangerschafts-spezifischen (pregnancy-specific) beta 1 glycoprotein (SP1). According to some characteristics (e.g. the molecular weight), the purified bPAG may correspond to a form of the pregnancy-specific protein B previously described by Sasser and colleagues (Biol Reprod 1986; 35:936-942).     

Plasmacytoid dendritic cells produce cytokines and mature in response to the TLR7 agonists,imiquimod and resiquimod

The immune response modifiers, imiquimod and resiquimod, are TLR7 agonists that induce type I interferon in numerous species, including humans. Recently, it was shown that plasmacytoid dendritic cells (pDC) are the primary interferon-producing cells in the blood in response to viral infections. Here, we characterize the activation of human pDC with the TLR7 agonists imiquimod and resiquimod. Results indicate that imiquimod and resiquimod induce IFN-alpha and IFN-omega from purified pDC, and pDC are the principle IFN-producing cells in the blood. Resiquimod-stimulated pDC also produce a number of other cytokines including TNF-alpha and IP-10. Resiquimod enhances co-stimulatory marker expression, CCR7 expression, and pDC viability. Resiquimod was compared throughout the study to the pDC survival factors, IL-3 and IFN-alpha; resiquimod more effectively matures pDC than either IL-3 or IFN-alpha alone. These results demonstrate that imidazoquinoline molecules directly induce pDC maturation as determined by cytokine induction, CCR7 and co-stimulatory marker expression and prolonging viability.