High-affinity binding of 125I-labeled mouse interferon to a specific cell surface receptor. IV. Mouse gamma interferon and cholera toxin do not compete for the common receptor site of alpha / beta interferon

Maternal recognition of pregnancy in the pig: A servomechanism involving sex steroids, cytokines and prostaglandins

Maternal recognition of pregnancy (MRP) is a term utilized in mammals to describe pathways in which the conceptus alters the endometrial environment to prevent regression of corpora lutea to ensure continued production of progesterone (P4) required for establishment and maintenance of pregnancy. For nearly 40 years after publication of the endocrine/exocrine theory, conceptus estrogen (E2) was considered the primary maternal recognition signal in the pig. Conceptus production of prostaglandin E2 (PGE2) was also considered to be a major factor in preventing luteolysis. An addition to E2 and PGE2, pig conceptuses produce interleukin 1B2 (IL1B2) and interferons (IFN) delta (IFND) and gamma (IFNG). The present review provides brief history of the discovery of E2, PGs and IFNS which led to research investigating the role of these conceptus secreted factors in establishing and maintaining pregnancy in the pig. The recent utilization of gene editing technology allowed a more direct approach to investigate the in vivo roles of IL1B2, E2, PGE2, AND IFNG for establishment of pregnancy. These studies revealed unknown functions for IFNG and ILB2 in addition to PGE2 and E2. Thus, pregnancy recognition signal is via a servomechanism in requiring sequential effects of P4, E2, IL1B2, PGE2 and IFNG. Results indicate that the original established dogma for the role of conceptus E2 and PGs in MRP is a far too simplified model that involves the interplay of numerous mechanisms for inhibiting luteolysis, inducing critical elongation of the conceptuses and resolution of inflammation in pigs.

Historical developments in the research of interferon receptors

Interferons (IFNs) were discovered 50 years ago independently by Isaacs and Lindemann and by Nagata and Kojima. When it was later realized that IFNs are active at very low concentrations, research began to determine how their powerful effects were generated from such a small initial signal. It has since been established that interferons, as well as all other cytokines, employ cell surface receptors to translate their presence in the serum to a potent cellular response to a viral infection. These receptor complexes are composed of multiple distinct glycosylated transmembrane polypeptides, a number of protein tyrosine kinases, and interact transiently with a large variety of other proteins including transcription factors, phosphatases, signaling repressors, and adaptor proteins coupling the receptor to alternative signaling pathways. Three major receptor complexes exist that are exclusive to each of three major classes of interferon. Even though the effects of each major class of interferon vary physiologically, each receptor complex interacts with its ligand in similar ways and activates similar signaling cascades. In this mini-review, we take a historical perspective at the major events in the characterization of interferon receptors, discussing interesting results that still need to be explained.

Fifty years of interferon research: aiming at a moving target

Nearly half a century has passed since the first published description of interferons (IFNs). This commentary introduces the four accompanying review articles on type I IFN research and attempts to relate how the field of IFN research has been changing during its history.

Hemin inhibits the interferon-beta-induced antiviral state in established cell lines

Hemin and other metalloporphyrins are known as very versatile compounds in nature, because they are able to carry out numerous functions in a free state or in association with specific proteins. When Friend murine erythroleukemia cells are treated with IFN-beta plus 100 microM hemin, the antiviral state is not observed, whereas the antiviral effect of IFN-gamma is unaffected by hemin treatment. This inhibitory effect of hemin is not restricted to erythroid cells. In fact, it is also observed in murine L929 and in human cell lines treated with IFN-beta. Neither trivalent iron in other forms nor hemin analogs (such as protoporphyrin IX or Sn(2+)-protoporphyrine IX) mimic this effect. Conversely, Co(3+)-protoporphyrin IX was as effective as hemin. At the transcriptional level, results obtained by run-on assays on nuclei from IFN-treated cells indicate that hemin does not completely inhibit IFN-beta induction of 2-5A synthetase gene(s) at 6 h of treatment but abolishes it at 24 h. In addition, hemin is able to inhibit the accumulation of IFN-induced 2-5A synthetase mRNAs. Experiments carried out to investigate the hemin effect on the early steps of the IFN signaling pathway indicate that hemin interferes with the ability of type I IFN to bind to its receptor, probably by a direct action on the IFN molecule.

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.

Posttranscriptional regulation of beta interferon expression in erythroid Friend cells treated with gamma interferon

Treatment of Friend erythroleukemia cells (FLC) with gamma interferon (IFN-gamma) in the presence of anti-IFN-beta antibodies reduces the effectiveness of the antiviral state and the induction of 2'-5'-oligoadenylate synthetase activity, indicating that the antiviral activity of IFN-gamma in FLC is in part mediated by the production of IFN-beta. Accordingly, IFN-gamma induces a less pronounced antiviral state in FLC resistant to IFN-alpha/beta than in wild-type cells. Moreover, while results of run-on assays indicate that both IFN-alpha and -beta genes are constitutively transcribed in these cells, FLC treatment with IFN-gamma induces only IFN-beta mRNA accumulation. These results indicate that posttranscriptional mechanisms are involved in the regulation of IFN-beta and -alpha expression by IFN-gamma. The low amounts of the induced IFN-beta synergize with IFN-gamma in mounting the potent antiviral effect.

Growth inhibitory effects of interferon-beta but not interferon-alpha on human glioma cells: correlation of receptor binding, 2',5'-oligoadenylate synthetase and protein kinase activity

The antiproliferative effects of human recombinant interferon-alpha (rIFN-alpha A) and interferon-beta (rIFN-beta ser) were assessed in vitro against seven human glioma cell lines. Further analysis of one of these lines (EFC-2) in response to rIFN-alpha A demonstrated a minimum growth inhibition by day 6 of treatment, whereas a 50% inhibition of cell growth was observed with a dose of 50 U/ml of IFN-beta ser. No significant growth inhibition was seen by rIFN-alpha A at doses up to 500 U/ml. Addition of rIFN-alpha A to rIFN-beta ser-treated EFC-2 cells neither suppressed nor augmented the antiproliferative response to IFN-beta ser. The binding of 125I-labeled rIFN-alpha A or 125I-labeled rIFN-beta ser to EFC-2 cells was inhibited competitively by increasing concentrations of either unlabeled rIFN-alpha A or rIFN-beta ser. This suggests that the cellular receptors for both rIFN-alpha A and rIFN-beta ser appear to be intact and appear to bind both agents equally. Furthermore, incubation of EFC-2 cells for 72 h with either rIFN-alpha A or rIFN-beta ser resulted in an increase in 2',5'-oligoadenylate (2-5A) synthetase activity 5-fold with rIFN-alpha A and 50-fold with rIFN-beta ser. Similarly, the 68-kD IFN-induced protein kinase was induced substantially with rIFN-beta ser but only slightly induced with rIFN-alpha A treatment. These results suggest that EFC-2 human glioma cells demonstrate a differential sensitivity in terms of growth inhibition to rIFN-beta ser and to rIFN-alpha A which appears to correlate with a differential induction of both intracellular 2-5A synthetase and protein kinase activity. These results cannot be explained solely on the basis of surface receptor binding of rIFN-alpha A and rIFN-beta ser. These data do suggest that, for human glioma cells in culture, type I IFN receptors may display a subtle architectural variation that allows equivalent binding of both IFN-alpha and IFN-beta ser, but allows an enhanced signal transduction and biological effect only after binding a specific IFN subtype.

Antitumor effect of combination of murine recombinant interferon beta, murine recombinant interferon gamma and human recombinant interleukin-2 in MethA-bearing mice

We have previously reported that the combination of murine recombinant interferon beta (Mu-rIFN beta) with murine recombinant interferon gamma (Mu-rIFN gamma) provided greater inhibition of tumor growth than did each one alone in MethA-bearing mice. In the present study the effect of addition of human recombinant interleukin-2 (Hu-rIL-2) to the combination of Mu-rIFN beta with Mu-rIFN gamma on tumor growth in BALB/c mice bearing syngeneic MethA fibrosarcoma was examined. Low doses of Hu-rIL-2 (5 x 10(3) U or 5 x 10(4) U at 3-day intervals) showed no antitumor activity, while a high dose of Hu-rIL-2 (5 x 10(5) U) showed profound growth inhibition. The administration of IL-2 (ranging between 5 x 10(3) U and 5 x 10(5) U) in addition to the combination of IFN beta and IFN gamma showed more augmented antitumor effects in a dose-dependent manner. Furthermore, the simultaneous administration of IL-2, IFN beta and IFN gamma had more effective therapeutic activity, compared with the sequential administration of interferons and IL-2. These findings indicated that IL-2 in combination with IFN beta and gamma was effective for cancer treatment.

Beta and gamma interferons act synergistically to produce an antiviral state in cells resistant to both interferons individually

We showed previously that the mouse fibroblastoid cell line Ltk-aprt- is resistant to the antiviral effects of beta interferon. This lack of response reflects a partial sensitivity to the interferon that is accompanied by a failure to activate expression of several interferon-regulated genes, although certain other genes respond in a normal manner. We show here that Ltk-aprt- cells were also unable to establish an antiviral state and to activate expression of 2,5-oligo(A) synthetase when treated with gamma interferon. Strikingly, however, treatment with a combination of beta interferon and gamma interferon provided complete protection against viral replication. Although the cells were completely insensitive to up to 250 U of the interferons per ml added singly, essentially complete protection from viral cytopathic effects was achieved when as little as 10 U of each of the interferons per ml were combined. Expression of 2,5-oligo(A) synthetase was also sensitive to this synergistic effect. Activation of an antiviral state could also be achieved by sequential treatment, first with gamma interferon and then with beta interferon. Partial protection against viral replication could be achieved by pretreatment with gamma interferon for as little as 1 h before incubation with beta interferon and could be blocked by the addition of specific antibodies or by cycloheximide, indicating that gamma interferon induces the synthesis of a protein which can act synergistically with a signal produced by the beta-interferon receptor. We suggest that Ltk-aprt- cells suffer from defects in one or more components of the gene activation pathways for both type I and type II interferons. Nonetheless, gamma interferon is able to activate the expression of a gene encoding a protein required for signal transduction. This protein acts synergistically with a transient signal produced in response to beta interferon, thereby activating the expression of a further group of genes.

Interferon receptors during treatment of chronic hepatitis B with interferon

The in vitro binding of 125I-labelled human alpha-interferon to peripheral blood mononuclear cells from 13 patients with chronic hepatitis B during interferon therapy was assayed in order to identify changes in the number of interferon receptors during treatment. Nine patients were treated with human alpha-interferon (Hu alpha-IFN) or human beta-interferon (Hu beta-IFN) daily for 4 weeks. During therapy, receptor sites per cell decreased by 40%. Two weeks after therapy ceased, this number had returned to the pretreatment level. The other four patients were given Hu alpha-IFN daily for 2 weeks, no injections for 2 weeks, and daily injections for 2 weeks. During both periods of therapy, receptor sites decreased by 40%. The number increased to 94% of the pretreatment level 1 week after the first period and to 101% 2 weeks later. It was 80% 1 week after the second period of injections and 108% 2 weeks later.

Comparison of the inhibitory effects of interferons-alpha and -gamma on testosterone production in porcine Leydig cell culture

In porcine Leydig cell culture, incubation with natural or recombinant human interferon-alpha (IFN-alpha), or recombinant porcine IFN-gamma preparations were effective in inhibiting basal and human chorionic gonadotropin (hCG)-stimulated testosterone production in a dose-dependent manner. Combined treatment with any of the human IFN-alpha preparations plus recombinant porcine IFN-gamma at the maximal inhibitory dose (1,000 pmoles/liter) further increased the inhibitory effect of any single IFN preparation on hCG-stimulated testosterone production. These results show that in porcine Leydig cells, both human IFN-alpha and porcine IFN-gamma are able to inhibit testosterone production and that the inhibitory action can be enhanced significantly by combined treatment with these types of IFNs. The enhancement of the inhibitory effect by combined treatment is consistent with the known presence of distinct cell membrane receptors for IFN-alpha and IFN-gamma.

Studies on the role of the 2'-5'-oligoadenylate synthetase-RNase L pathway in beta interferon-mediated inhibition of encephalomyocarditis virus replication

Interferons inhibit the replication of vesicular stomatitis virus (VSV), but not of encephalomyocarditis virus (EMCV), in mouse JLSV-11 cells. We report the isolation of clonal derivatives from this cell line in which the replication of both viruses is impaired by interferons. These clones were selected from the parental line by virtue of their rescue by interferon treatment from the cytopathic effects of EMCV infection. In one such clone, RK8, the replication of VSV and EMCV and the production of resident murine leukemia virus were inhibited by interferon. On the other hand, in clone RK6, which was isolated without any selection, the replication of VSV, but not of EMCV, was impaired by interferons. The levels of 2'-5'-oligoadenylate synthetase mRNA and enzyme activity were similarly elevated upon interferon treatment in the two clones. However, the level of RNase L, as determined by binding and cross-linking of a radiolabeled 2'-5'-oligoadenylate derivative, was much lower in RK6 cells than in RK8 cells. In accord with this observation, the introduction of 2'-5'-oligoadenylates into cells inhibited protein synthesis much less strongly in RK6 cells than in RK8 cells. These results are consistent with the notion that the 2'-5'-oligoadenylate-dependent RNase L may be a mediator of the inhibition of EMCV replication by interferons.

Reduction of transferrin receptor expression by interferon gamma in a human cell line sensitive to its antiproliferative effect

Interferon gamma (IFN gamma) reduced 125I-transferrin binding to WISH cells which are sensitive to its antiproliferative effect. IFN gamma did not affect transferrin binding to Daudi cells or phytohemagglutinin-stimulated human lymphocytes, neither of which respond to its antigrowth action. Scatchard analyses of the equilibrium binding of 125I-transferrin to WISH cells exposed to IFN gamma revealed a decrease in the number of cell surface receptors but no change in the apparent association constant compared with control cells. When 125I-transferrin binding was measured using detergent-extracted cells, the IFN-induced reduction of binding was smaller than with intact cells. This suggests that in WISH cells, IFN gamma not only reduced the total number of transferrin receptors, but also modified the process of receptor internalization and recycling. Labeling of newly synthesized receptors with [35S]-methionine indicated that a reduction in the biosynthesis might account for the decrease in the total number of transferrin receptors in IFN gamma-treated cells. Our results suggest that the antigrowth effect of IFN gamma is at least partly due to its inhibitory action on transferrin receptor expression leading to iron starvation.

Characterization of L1210 S cells with low sensitivity to mouse interferon-gamma

A mouse leukemic cell line L1210 Sg with a low sensitivity to interferon-gamma (IFN-gamma) was described. On the nature of the antiviral action and binding of IFN, L1210 Sg cells were compared with L1210 m cell line which is sensitive to IFN-gamma. For a half reduction of the vesicular stomatitis virus-RNA synthesis, L1210 Sg cells required 500-fold more IFN-gamma than L1210 m cells did. However, both cell lines were induced to the antiviral state to the same extent with IFN-alpha or -beta. L1210 Sg and L1210 m cells were sensitive to the anti-proliferative action of IFN-alpha and -beta, but insensitive to IFN-gamma. (2'-5')Oligoadenylate synthetase was induced in these cell lines by IFN-beta, but not by IFN-gamma, which suggests that the induction of this synthetase may not be responsible for the antiviral action of IFN-gamma. No substantial difference between L1210 Sg and L1210 m cells was found in IFN receptors for IFN-gamma and IFN-beta either in number per cell or in their affinity to corresponding IFN type. However, differences were noted in time course profiles of cell-associated IFN-gamma at 37 C: in L1210 m cells, a rise-and-decay profile of IFN-gamma bound to cells was observed at 37 C, but in L1210 Sg cells, rise and slight decay was observed. On the other hand, a similar rise-and-decay curve of IFN-beta bound to these cells was observed. These results indicated that the low sensitivity of L1210 Sg cells to IFN-gamma may be due to this slight decay of receptor-bound IFN-gamma.

Interferons-alpha/beta- and -gamma-resistant Friend cell variants exhibiting receptor sites for interferons but no induction of 2-5A synthetase and 67K protein kinase

A number of Friend leukemia cell variants with a interferon-gamma (IFN-gamma)-resistant phenotype have been isolated. They appear resistant to the antiproliferative action of IFN-gamma and to the induction of the antiviral state assessed by Friend leukemia virus release and vesicular stomatitis virus yield. Selection was performed via a prolonged exposure to increasing amounts of highly purified recombinant IFN-gamma of wild-type Friend cells or of variant clones thereof already resistant to IFN-alpha/beta (Affabris et al., 1982, Virology 120, 441-452). Only the clones derived from IFN-alpha/beta-resistant variants showed a phenotype fully resistant to IFN-gamma treatment while keeping their previously acquired resistance to IFN-alpha/beta. These cells are not deficient in high-affinity receptors for IFN-gamma so that their resistant phenotype appears to be mediated by events distal to binding of IFN-gamma to its receptors. Furthermore, analysis of IFN-induced dsRNA-dependent 2-5A synthetase and 67K protein kinase enzymatic activities, biochemical markers for cellular responses to IFN, showed that both these activities were not induced in IFN-alpha/beta and IFN-gamma-resistant clones when treated with either type of IFN. Accordingly, no increased expression of 2-5A synthetase mRNA(s) could be detected by probing poly(A)+-enriched RNA from cells exposed to IFN-alpha/beta or IFN-gamma treatment with murine or human specific cDNAs. On the other hand, no major changes in restriction patterns of 2-5A synthetase gene(s) were observed in these variant cells by restriction endonuclease digestion and Southern blotting. In addition, analysis of 2-5A synthetase mRNA induction, performed on wild-type cells, showed that the kinetic of induction due to IFN-gamma treatment is slower than that obtained with IFN-alpha/beta.

Growth inhibitory effect of recombinant alpha and beta interferon on human glioma cells

Growth inhibitory activity of recombinant alpha and beta interferon on two human glioma cell lines, EFC-2 and KE cells, was determined by two different growth assays. Recombinant beta interferon showed a slight growth inhibitory effect on EFC-2 cells at day 3, and maximum inhibition was seen on day 6 with an ID50 of 50 U/ml. Recombinant alpha interferon showed no significant growth inhibition at any concentration. KE cells were resistant to both recombinant alpha and beta interferon. The growth inhibitory activity of recombinant beta interferon on EFC-2 cells was not blocked by recombinant alpha interferon, although recombinant alpha and beta interferons shared same receptors on EFC-2 cells. Addition of DFMO (alpha-difluoromethylornithine) to interferon in the media showed additive effect rather than synergistic effect in growth inhibition of glioma cells. Out of 7 glioma cell lines tested, 4 showed heterogeneous sensitivity to recombinant beta interferon, and all were resistant to recombinant alpha interferon. These results suggest a differential sensitivity of EFC-2 cells to recombinant beta interferon, as well as a heterogeneous sensitivity to recombinant beta interferon among different glioma cell lines.

Induction of major histocompatibility class I antigens by interferons in undifferentiated F9 cells

Mouse embryonal carcinoma F9 cells, upon treatment with interferons (IFNs), express major histocompatibility (MHC) Class I antigens, which are otherwise not expressed in these cells. Both IFN-gamma and IFN-alpha/beta increase the steady-state level of Class I mRNA within 60 min of the treatment which leads to the subsequent surface expression of the H-2Kb and H-2Db antigens, suggesting that undifferentiated F9 cells express IFN receptors. IFNs induce Class I antigen expression in F9 cells in a highly selective manner: unlike retinoic acid treatment which also stimulates the antigen expression, IFNs induce neither morphological differentiation, increased binding of epidermal growth factor, nor reduction of expression of stage specific embryonic antigen. The effect of IFNs is reversible; removal of IFNs, even after prolonged exposures, results in a rapid loss of the Class I gene expression. Further, Class I mRNA induction is not inhibited by cycloheximide, suggesting possible independence from de novo protein synthesis. This Class I antigen induction in F9 cells is reminiscent of that observed in somite stage mouse embryos by IFN treatment and may offer a model system to study activation of MHC genes during development.

Nonidentical induction of the guanylate binding protein and the 56K protein by type I and type II interferons

Upon the addition of interferon (IFN) to cultured human cells, the expression of genes encoding the 56K and the guanylate binding protein (GBP) is specifically induced. We have analyzed their expression at the protein and the mRNA levels and studied how their regulation differs in cells treated with different IFNs. In the type I IFN (alpha and beta)-treated cells, we detected the accumulation of the 56K protein primarily in the cytoplasm. The 56K protein was undetectable in untreated cells or in cells treated with type II IFN (IFN-gamma). In contrast, a greater amount of GBP was synthesized in cells treated with type II IFN than in cells treated with type I IFN. The differential induction of these two proteins correlates well with the relative amounts of their mRNAs in type I and type II IFN-treated cells. In addition, the IFN-induced synthesis of the 56K protein was found in certain cell lines in which the GBP synthesis was not detected. These results suggest that the regulation of these two genes requires dissimilar factors which are activated or induced to different extents by type I and type II IFNs.

Inhibition of murine L cell interferon action by heparin

Heparin added together with murine L cell interferon inhibited the development of antiviral activity in mouse L cells. When added after interferon treatment, heparin had no effect on antiviral activity. There was also no inhibition of interferon action in L cells treated with heparin before addition of interferon. On the other hand, heparin did not inhibit antiviral activities of human interferon alpha and beta. Since murine L cell interferon, but not human interferon alpha and beta, binds to a heparin affinity column and can be eluted with a solution of high salt, it is presumed that murine L cell interferon and heparin must interact with each other. The apparent interaction of heparin with murine L cell interferon was prevented by protamine, a drug that neutralizes heparin. Dextran sulfate inhibited murine L cell interferon action, but dextran and chondroitin sulfate A did not. These results suggests that heparin inhibited murine L cell interferon action by the binding via sulfate groups on its molecules. Heparin also inhibited antiviral activity of murine L cell interferon in mice infected with herpes simplex virus (+GC Miyama strain).

The interferon receptors

Early studies on the mode of action of interferons have indicated that a receptor system on the cell surface is involved in its action. The first direct evidence to a high-affinity binding site was found only after pure interferon was available. Two different receptors, one specific for interferons-alpha and beta, and the other for interferon-gamma were recognized. A correlation between affinity to the receptor and specific activity was established. Cross-linked complexes of labeled interferons with their receptors were visualized on gel electrophoresis and even partially purified. Internalization of interferons after binding to the receptor was reported. The role of gangliosides as helpers of interferon binding was recently investigated. Fragments of interferons which still retained binding capacity were described and helped in elucidating the binding site on the interferon molecule.

Leukocytes from multiple sclerosis patients respond to alpha- and gamma-interferons

Blood mononuclear leukocytes from multiple sclerosis (MS) patients were evaluated for reactivity to alpha- or gamma-interferon (IFN), using a response whereby IFN-treated (primed) cells synthesize higher levels of IFN than untreated cells. Leukocytes were treated in vitro with natural alpha-IFN, recombinant alpha-IFN, recombinant gamma-IFN, or no IFN, then exposed to measles virus to induce IFN synthesis. With no IFN treatment, IFN production by cells from the MS patients was significantly less than normal (P less than or equal to 0.025). However, with IFN treatment, cells from MS patients were primed as well as cells from normal controls: IFN synthesis for the MS patients' cells was increased 10-11-fold with either alpha-IFN preparation and 3.6-fold with gamma-IFN. These findings verify the presence of leukocyte reactivity to alpha-IFN and provide the first demonstration of responsiveness to gamma-IFN in MS.

Biological activity of liposome-encapsulated murine interferon gamma is mediated by a cell membrane receptor

Recombinant murine gamma interferon (rMuIFN-gamma) was found to bind reversibly to a specific high-affinity surface receptor on L929 cells; neither murine alpha or beta nor human gamma IFN competed for receptor binding. Encapsulation of the rMuIFN-gamma in either negatively or positively charged liposomes reduced its immediate ability to bind to this surface receptor. Disruption of liposome integrity with detergent resulted in full ability of the rMuIFN-gamma to bind to the membrane receptor. Incubation of the liposomal IFN in serum-containing medium resulted in significant leakage so that the IFN was able to bind to its surface receptor. Assessment of the biological activity of the rMuIFN-gamma preparations revealed that full antiviral activity was observed in vitro with the liposomal IFN preparations without their prior disruption by detergent. The antiviral activity observed with either free or liposomal IFN was neutralized completely by antibodies against rMuIFN-gamma. Both free and liposomal rMuIFN-gamma, in conjunction with bacterial lipopolysaccharide, were also able to activate murine peritoneal macrophages to the tumoricidal state. Again, this activity of both free and liposomal IFN could be neutralized completely by antibody. These results indicate that although rMuIFN-gamma can be effectively incorporated into liposomes, it must ultimately leak out of the liposome in order to mediate its biological effects; these effects are triggered after the IFN binds to its cell surface receptors.

Antibodies to chromosome 21 coded cell surface components block binding of human alpha interferon but not gamma interferon to human cells

Antisera raised against a human X mouse hybrid cell line containing human chromosome 21 as its only human chromosome, block induction of an antiviral state by human alpha interferon (IFN-alpha), block induction of (2'-5')oligoisoadenylate synthetase [2'-5')A synthetase), and block binding of 125I-labeled and 35S-labeled recombinant, human IFN-alpha A, but not 125I-labeled IFN-gamma, to cell surface receptors. The data presented clearly demonstrate that the cell surface receptors for IFN-alpha and IFN-gamma are different, and provide independent evidence of the role of a chromosome 21 coded cell surface molecule in the pathway to the generation of the antiviral state.

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.

Synergistic antiviral and antiproliferative activities of Escherichia coli-derived human alpha, beta, and gamma interferons

The antiviral and antiproliferative effects of highly purified Escherichia coli-derived human interferons (IFNs) were examined in human melanoma cells (Hs294T). Antiproliferative activity was monitored by measuring inhibition of cell multiplication, and antiviral activity was determined by inhibition of herpes simplex virus type 1 replication. Treatment of cells with IFN-gamma in combination with IFN-alpha A or IFN-beta 1 resulted in potentiation of both antiproliferative and antiviral activities. In contrast, combination treatments composed of IFN-alpha A and IFN beta 1 yielded inconsistent results. Some combinations reflected additive responses, whereas others were antagonistic. To examine correlations between IFN-induced biological activities and interactions of the different IFNs with cell surface receptors, in vivo [35S]methionine-labeled IFN-alpha A was prepared. Binding studies indicated the presence of 2,980 +/- 170 receptors per cell, each with an apparent Kd of (8.4 +/- 1.3) X 10(-11) M. Results from competitive binding studies suggested that Hs294T cells possess at least two types of IFN receptors: one which binds IFN-alpha A and IFN-beta 1 and another to which IFN-gamma binds.

Mx-dependent resistance to influenza viruses is induced by mouse interferons alpha and beta but not gamma

In cells derived from congenic BALB.A2G-Mx mice carrying the resistance gene Mx, but not in cells from BALB/c mice lacking Mx, mouse interferons alpha and beta induced the synthesis of a unique cellular protein that was associated with an efficient antiviral state with selectivity for influenza viruses. In contrast, native or recombinant mouse interferon gamma failed to efficiently protect Mx-bearing cells against influenza viruses and did not noticeably induce the synthesis of the Mx-associated protein, although interferon gamma was as effective as interferons alpha and beta in protecting BALB.A2G-Mx and BALB/c cells against the rhabdovirus VSV. These results demonstrate that different types of interferons differentially regulate the expression of the Mx gene and thereby induce distinct antiviral states.

Various human interferon alpha subclasses cross-react with common receptors: their binding affinities correlate with their specific biological activities

Seven different human interferon (IFN) alpha subtypes were compared with regard to competitive inhibition of specific high-affinity binding of 125I-labeled IFN alpha-2 to human and bovine cells. All IFNs tested (alpha-1, -2, -4, -5, -6, -7, -8) competed for common binding sites. Marked differences in the binding affinities were observed between IFN alpha-1 and IFN alpha-2. The binding affinities of the various subtypes correlated with the respective specific biological activities determined in an antiviral assay. These observations suggest that at least some biological effects of IFNs are initiated by receptor activation and depend quantitatively on the degree of receptor saturation.

Type I and Type II interferon receptors

Binding site competition studies of 125I-interferon (IFN)-gamma were performed with homogeneous preparations of IFNs alpha 2, beta, and gamma. It was found that only IFN-gamma could compete for the specific binding site of 125I-IFN-gamma in both WISH and FS11 cells. Thus, a clear distinction between the receptor of IFN- alpha and beta on one hand, and the receptor of IFN-gamma on the other hand, was obtained. This result is unambiguous because all IFN preparations which were used were purified to homogeneity by specific monoclonal antibody immunoaffinity chromatography. We propose to assign the names "Type I" for the receptor of IFN-alpha and IFN-beta, and "Type II" for the specific receptor of IFN-gamma.

Decreased interferon synthesis and responsiveness to interferon by leukocytes from multiple sclerosis patients given natural alpha interferon

Despite the use of interferon (IFN) in numerous clinical trials, relatively little is known about how IFN therapy influences leukocyte function. To evaluate some of its effects, leukocytes from multiple sclerosis (MS) patients given daily treatments of natural alpha IFN (IFN-alpha) were evaluated for IFN synthesis and two responses to IFN in vitro: enhancement (priming) of IFN synthesis and suppression of Concanavalin A (Con A)-induced T-cell mitogenesis. The IFN therapy had no effect on the sensitivity of Con A-stimulated leukocytes to the antiproliferative action of IFN-alpha. However, using Newcastle disease virus (NDV), measles virus, or poly I:C to stimulate IFN synthesis, cells from IFN-treated patients produced less IFN in response to all inducers, with titers ranging between 11% and 44% of pretherapy values. Also, unlike cells from these same patients before therapy or from the placebo recipients, cells from the IFN recipients were not primed by either IFN-alpha or -beta even though IFN-beta had not been used for therapy. The loss of these priming reactivities suggests that resistance to IFN had developed in IFN-treated patients.

Studies on purification of human gamma interferon: chromatographic behavior of accompanying IL2 and B-cell helper activity

Gamma interferon (gamma IFN) was produced in human lymphocyte cultures stimulated by PHA. Titers were in the range of 10,000-30,000 U/ml. Crude gamma IFN was adsorbed on silicic acid, from which the antiviral activity was eluted by a buffer containing a high salt concentration and ethylene glycol. This treatment allowed quantitative recovery of gamma IFN with a specific activity of 5 X 10(5)-1 X 10(6) U/mg of proteins. IL2 and B-cell helper activities were adsorbed and eluted from silicic acid together with the antiviral activity. This finding might be of practical interest for the purification of these lymphokines, particularly IL2. Gamma interferon was further purified on Blue Sepharose to a specific activity of 2 X 10(7) U/mg. The resulting preparations still contained IL2 and B cell helper activities. However, taking advantage of the differences in apparent hydrophobicity and in isoelectric point, we were able to dissociate antiviral activity from lymphokines. Such dissociation should facilitate the study of the biological properties of human natural gamma IFN.

Action of different gamma interferons on mouse leukemic cells resistant to alpha and beta interferons

Phytohemagglutinin-induced interferon-gamma (IFN-gamma) was reported to act on mouse leukemic L1210 R cells resistant to IFN-alpha and -beta. Results reported here show that these cells are also sensitive to various preparations of murine IFN-gamma derived from different sources and purified to different degrees and that lymphokines present in the preparations are not involved in the antiviral effect of IFN. In addition, IFN-gamma preparation increases concanavalin A binding to L1210 S and L1210 R cells indicating that the sensitivity of L1210 R cells to IFN-gamma is not limited to its antiviral effect.

Characterization of an interferon receptor on human lymphoblastoid cells

A cell-free assay was developed to measure the binding of iodinated human interferon-alpha 2 to membranes prepared from lymphoblastoid Daudi cells. The kinetics of binding were similar at 0 degrees C and 30 degrees C, with 1.3-fold more interferon bound at the higher temperature. Membrane preparations treated with Triton X-100 proved to be a convenient source of solubilized receptor. An assay was developed to measure the binding of 125I-labeled interferon (125I-interferon) to solubilized receptors, based on the precipitation of interferon-receptor complexes with polyethylene glycol. Optimal binding with this assay was obtained at 0 degrees C. The solubilized receptor was analyzed by zonal sedimentation centrifugation and gel filtration. Sedimentation analysis in H2O and 2H2O gradients provided the sedimentation coefficient and the partial specific volume of the receptor-Triton X-100 complex. Gel filtration chromatography provided the Stokes radius of this complex. From these data we calculated several physical parameters, including Mr = 95,000 for the protein portion of the complex. The receptor is a highly asymmetric and hydrophobic membrane protein. 125I-Interferon could be crosslinked to receptors of intact Daudi cells or of isolated membranes by use of disuccinimidyl suberate. The covalently linked 125I-interferon-receptor complexes were analyzed by gel electrophoresis. A single band with Mr = 140,000 was detected in gel autoradiographs. If one molecule of interferon is present in this complex, the Mr of the receptor is close to 120,000. Possible reasons for the different Mr values obtained with the two analytical procedures used are discussed.

Isolated interferon alpha-receptor complexes stabilized in vitro

We describe the extraction and stabilization in vitro of discrete complexes of interferon and cellular receptor proteins. A homogeneous complex of Mr 230 000 was extracted at the time of peak receptor binding (30 min). Complex formation was specific for human interferon. At later times a second complex could also be extracted suggesting transfer of interferon to a second site.

Ultrastructural distribution of interferon receptor sites on mouse L fibroblasts grown in suspension: ganglioside blockade of ligand binding

Murine beta-interferon (IFN) receptors on L929 cells grown in suspension culture were visualized by indirect immunoferritin electron microscopy. Ferritin label on these cells was associated primarily with the coated areas and coated pits of the membrane, in contrast to previous observations with L929 cells grown in a monolayer, which did not reveal such coated areas or pits but showed ferritin label distributed randomly on the cell membrane (Kushnaryov et al., Infect. Immun. 36:811-821, 1982). On about 15% of the cell sections from suspension-grown cells, the ferritin label was found outside coated membrane areas. These findings suggest that different cell populations exist with respect to the localization and possibly the affinity of IFN receptors. In the same experiment, exogenously added gangliosides blocked the binding to cell surfaces not only of 125I-labeled IFN but also of unlabeled IFN as revealed by an immunospecific ferritin labeling technique, providing direct evidence that gangliosides interfere with the binding of IFN to specific receptor sites on the surface of mouse L929 cells. These studies establish that the binding of IFN to cell membranes, depending on cell growth conditions, can involve coated areas and coated pits, to which certain hormones and toxins have been shown to bind.

Binding of human interferon alpha to cells of different sensitivities: studies with internally radiolabeled interferon retaining full biological activity

The characteristics of interferon binding to various cells with different interferon sensitivity were studied by using [3H]leucine-labeled, pure human interferon alpha from Namalwa cells. Scatchard analysis of the binding data on cells sensitive to interferon alpha (human FL and fibroblasts and bovine MDBK) indicated the presence of two kinds of binding sites with high and low affinities. The binding constants of the high-affinity sites in these cells were similar (4 X 10(10) to 11 X 10(10) M-1). Cells insensitive to human interferon alpha (human HEC-1 and mouse L cells) were shown to have only low-affinity sites, suggesting that high-affinity binding sites are indispensable for interferon sensitivity and represent interferon receptors. However, the number of sites in three human diploid fibroblast strains and one strain trisomic for chromosome 21 were not proportionally correlated to the interferon sensitivity of the cells. The high-affinity binding to human cells was completely inhibited by both nonradioactive human interferons alpha and beta in a similar manner, but binding to bovine MDBK cells, on which human interferon beta is practically inactive, was inhibited effectively only by interferon alpha and not by beta. These results suggest that the receptor for human interferon alpha is common to human interferon beta in human cells, whereas the receptor on bovine cells binds only human interferon alpha.

A unique set of polypeptides is induced by gamma interferon in addition to those induced in common with alpha and beta interferons

Human immune interferon (IFN-gamma) differs from leukocyte interferon (IFN-alpha) and fibroblast interferon (IFN-beta) in cell origin, inducing agents, physical and biological properties and amino acid sequence. These differences have led to interest in possible differences in the biological properties of IFN-gamma compared with IFN-alpha and IFN-beta. IFN-gamma has the same broad range of biochemical and biological actions as do IFN-alpha and IFN-beta, although relative potencies vary depending on the cell type and function investigated. There has so far been no direct evidence that IFN-gamma alters normal cell functions differently from other interferons. We report here striking qualitative and quantitative differences in the intracellular response of human fibroblasts to IFN-gamma compared with IFN-alpha and IFN-beta. Two-dimensional gel electrophoresis demonstrates, in addition to the induction of a common group of polypeptides, the existence of a set of polypeptides whose synthesis is uniquely induced by IFN-gamma.

Human interferon-alpha-and-gamma-mediated inhibition of retrovirus production in the absence of an inhibitory effect on vesicular stomatitis virus and encephalomyocarditis virus replication in RD-114 cells

RD-114 line is a human sarcoma cell line chronically infected with RD-114 retrovirus. Treatment of these cells with increasing doses of human interferon-alpha or -gamma resulted in increasing inhibition of RD-114 virus production. Surprisingly, the replication of vesicular stomatitis virus and encephalomyocarditis virus, in these cells and in the parental RD cells which are not infected with the retrovirus, was insensitive to interferon treatment. Unlike reported differences in other properties of interferon-alpha and interferon-gamma, there were no differences in their antiretroviral properties such as dose response, kinetics of establishment of the antiretroviral state, and kinetics of its dissipation upon removal of interferon.