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

Generation and characterization of anti-idiotypic antibodies recognizing the interferon-alpha receptor: implications for ligand-receptor interactions

Monoclonal antibodies LI-1 and LI-8 against interferon-alpha A (IFN-alpha A) block IFN-alpha A activity and binding to its receptor, but they recognize distinct epitopes. Surprisingly, anti-idiotypic antibodies to both LI-1 and LI-8 have properties consistent with recognition of the receptor: anti-LI-1 and anti-LI-8 antibodies inhibit the binding of IFN-alpha A to its receptor. However, anti-LI-1 is an antagonist of IFN-alpha A, while anti-LI-8 is an agonist. Thus, at least some part of the epitopes on IFN-alpha A recognized by LI-1 and LI-8 are directly involved in receptor binding. Because these epitopes are spatially distinct, the implication is that the receptor binding site on IFN-alpha A must be extensive, or there are minimally two regions of IFN-alpha A involved in receptor interactions.

Specific antiviral activities of the human alpha interferons are determined at the level of receptor (IFNAR) structure

Differences in activity among the family of human IFNs alpha are much reduced if these ligands are assayed on bovine cells. In particular, the activity of IFN alpha D is much higher on bovine than on human cells. To examine these differences, the bovine counterpart of the human IFNAR has been cloned and expressed in a human cell line. The transfected cell line now recognizes the human IFN alpha D as a high-specific-activity IFN subtype, indicating that the differences in sensitivity between the bovine and human cells to the human IFN alpha lie in the structure of the IFNAR chain rather than in the other components of the functional receptor.

Interferon-alpha suppresses the capacity of T cells to help antibody production by human B cells

This study was designed to analyze the effect of interferon-alpha (IFN-alpha) on the potential of T cells to help B-cell differentiation in vitro. Human splenic T cells preactivated via the T-cell receptor (TCR)/CD3 complex, as well as murine EL4 thymoma T cells preactivated with phorbol esters, stimulated human B cells via a species cross-reactive physical interaction to differentiate into antibody-producing cells. If the human or murine T cells were activated in the presence of IFN-alpha, normal proliferation and interleukin-2 (IL-2) production occurred, but the cells did not acquire any B-cell helper potential. Therefore, IFN-alpha modulates the B-cell stimulatory potential of T cells by interfering with the T-cell activation process. In contrast, IFN-alpha neither acted on B cells directly nor on already activated T cells, because it did not suppress B-cell differentiation induced by T cells preactivated in the absence of IFN-alpha. IFN-alpha did not induce the production of inhibitory T-cell factor(s), since T cells preactivated in the presence of IFN-alpha did not inhibit the interaction of B cells with T cells optimally preactivated in the absence of IFN-alpha. Taken together the data indicate that IFN-alpha suppresses the potential of T cells to stimulate B-cell differentiation by interfering with the T-cell activation process, but acts neither on B cells directly nor on already activated T cells.

Structure of the human interferon alpha receptor

The structure of the IFN alpha receptor has been studied by methods such as affinity crosslinking and gel chromatography over the last 8 years. The recent development of monoclonal antibodies against the receptor, and the cloning of an IFN alpha receptor cDNA has provided new important tools to understand the IFN alpha receptor structure. Thus, it has become obvious that the IFN alpha receptor has a more complex structure than first anticipated, probably involving more than one subunit. This review analyzes the present knowledge about the structure of the IFN alpha receptor, as well as many unresolved issues concerning this topic.

Effects of recombinant human alpha A interferon in gnotobiotic calves challenged with respiratory syncytial virus

The effects of recombinant human alpha A interferon were studied in gnotobiotic calves challenged with respiratory syncytial virus (RSV). Gnotobiotic calves given doses of interferon by intramuscular injection over five days showed a marked, dose-related, rise in rectal temperature and depression of circulating leucocytes. Differential counts showed decreases in both lymphocytes and neutrophils. No significant pathological differences were found between treated and untreated calves, nor could any difference be demonstrated in the pattern of RSV infection.

Structure-function studies of human interferons-alpha: enhanced activity on human and murine cells

To identify functionally important regions of the human interferon (IFN)-alpha molecule, mutagenesis in vitro of human IFN-a genes was used to create analogs with deletions or specific amino acid replacements. These analogs were expressed in vitro using SP6 RNA polymerase and a rabbit reticulocyte lysate protein synthesis system. Deletion of 7 highly conserved hydrophilic amino acids from the C-terminus of human IFN-alpha 4 reduced, but did not abolish, antiviral activity on human cells. However, analogs with deletions of 15 or 25 amino acids from the C-terminus, or 28 amino acids from the N-terminus, had no measurable antiviral activity. The antiviral activity of human IFN-alpha 4 was increased by substitution of cysteine for serine at position 86, and lysine for arginine at position 121. However, other amino acid substitutions at positions 121, 122 or 123 reduced antiviral activity. The size of the side chain of the amino acid residue at position 130 was shown to be important. Replacement of the absolutely conserved leucine residue at position 131 with glutamine had little effect on antiviral activity. However, the introduction of a proline residue at this position abolished antiviral activity, probably due to the formation of a beta turn in the polypeptide chain. The antiviral activity of human IFN-alpha 4 on murine cells was increased by substitutions at positions 86, 121 and 133. This study illustrates the utility of the in vitro mutagenesis and rabbit reticulocyte lysate systems for the investigation of structure-function relationships, and extends our knowledge of the biologically active regions and species specificity of the human IFN-alpha molecule.

Three human interferon-alpha 2 subvariants disclose structural and functional differences

The human interferon-alpha 2 subvariants 2a, 2b and 2c differ by only one or two amino acids at positions 23 and/or 34 of the mature protein. In this study, the coding regions of the three interferon-alpha 2 subvariants were derived from the cDNA of interferon-alpha 2c by site-directed in vitro mutagenesis. The interferon-alpha subvariants were synthesized using the same Escherichia coli strain for production and were subsequently purified. Comparative studies revealed that they differ significantly in their biological and antigenic properties. Therefore, amino acid positions 23 and 34 seem to be crucial for structure/function of human interferon-alpha. Furthermore, the study points to the importance of defining, whether such minor structural variants of naturally occurring polypeptides represent functional variants.

The development of liposomes containing interferon alpha for the intravesical therapy of human superficial bladder cancer

Current therapy of human superficial bladder cancer includes the intravesical administration of antitumor drugs and immunomodulators. The purpose of these studies was to determine whether phospholipid liposomes that bind to human bladder cancer cells can improve the delivery of interferon alpha (IFN-alpha) to neoplastic urothelium. The antiproliferative activity of free IFN-alpha and IFN-alpha encapsulated in liposomes was assessed in vitro against the human transitional cell carcinoma line 253J. The cells were exposed to free and liposome-encapsulated IFN-alpha for short periods ranging from 30 minutes to four hours, and inhibition of cell growth was determined three days later. The production of greater than 25 percent cytostasis of 253J cells by free IFN-alpha required four hours of continuous exposure. In contrast, IFN-alpha encapsulated in liposomes produced 35 percent and 60 percent cytostasis after a 30-minute and four-hour exposure, respectively. Liposome-encapsulated IFN-alpha was also effective (50 percent cytostasis) against a subline of 253J cells selected for resistance against free IFN-alpha. Liposomes containing IFN-alpha were stable in the presence of human urine. In vivo studies in mice showed that intravesical administration of radiolabeled IFN-alpha or radiolabeled liposomes did not yield significant systemic absorption and deposition in distant organs. Collectively, these results suggest that the encapsulation of IFN-alpha within multilamellar liposomes may augment its antiproliferative activity, overcome some forms of tumor cell resistance to IFN-alpha, and prove useful for intravesical therapy of superficial bladder cancer.

Genetic transfer of a functional human interferon alpha receptor into mouse cells: cloning and expression of its cDNA

A cDNA coding for the human interferon alpha receptor has been cloned using a gene transfer approach. This consists of transferring human DNA to mouse cells and selecting for cells sensitive to human interferon alpha. The transfected cells expressed the human interferon alpha receptor, and a 5 kb human DNA was isolated from a secondary transfectant. This DNA defects an mRNA present in human cells and was used to clone a 2.7 kb cDNA from a library constructed from human Daudi cells. The sequence of the cDNA is presented. It codes for a glycoprotein of 557 amino acids with an N-terminal hydrophobic region and a single transmembrane-spanning segment. Mouse cells expressing the cDNA become sensitive to the antiviral activity of and express binding sites for human interferon alpha, demonstrating that the cloned cDNA encodes a functional human interferon alpha receptor.

Molecular characterization of the human interferon-gamma receptor: analysis of polymorphism and glycosylation

Different molecular masses have been assigned to the human interferon-gamma receptor (HuIFN-gamma-R) by several authors. After extensive purification from Raji cells, this receptor was shown in a previous work to consist of two major protein species with molecular masses of 92 kD and 50 kD, as revealed by SDS-PAGE. We show here that the 50-kD band is most probably a degradation product of the 92-kD band due to a trypsin-like protease active during the purification process. The native protein of Raji cells seems, therefore, to have a molecular mass of 92 kD. The same molecular mass was found with Colo 205 cells (derived from a colon carcinoma). However, in conditions where degradation does not occur, the HuIFN-gamma-R shows a certain polymorphism: in IM-9 cells, another B-cell line, two bands exist with molecular masses of 95 kD and 85 kD, and in Wish cells, an amnion-derived cell line, one (or two) band(s) can be detected around 87 kD. This polymorphism is due at least in part to a variable extent of N-glycosylation from line to line and also within the same line, since after tunicamycin treatment of the Raji, IM-9, and Wish cells, very similar bands are obtained with a molecular mass of 72 kD.

Rat but not human interferons suppress hepatic oxidative drug metabolism in rats

An animal model suitable for in vivo studies of interferon-mediated suppression of hepatic oxidative drug metabolism has been developed. Rats were injected with either recombinant human interferon alpha A, recombinant human interferon gamma, recombinant rat interferon gamma, or vehicle and experiments were performed 24 h later. In some animals theophylline elimination was determined twice (10 days apart), once after interferon and once after vehicle. Theophylline clearance was also determined in the isolated perfused rat liver after pretreatment of animals with interferon or vehicle. Pretreatment of animals with rat interferon gamma significantly reduced theophylline clearance in the intact rat but neither human interferon alpha A nor human interferon gamma altered theophylline elimination in vivo. Similar results were observed in the isolated perfused rat liver. We then examined whether the effects of interferon on hepatic drug metabolism were generalized or confined to individual cytochrome P450 isozymes; androstenedione hydroxylation pathways were used as catalytic probes for individual cytochrome P450 isozymes. Rat interferon gamma (but not human interferon alpha A) decreased levels of total hepatic microsomal P450 and reduced androstenedione 16 beta-hydroxylation. The formation of three other hydroxylated androstenedione metabolites appeared reduced to a similar extent, although these changes were not significant. It is concluded that autologous but not heterologous interferons impair oxidative drug metabolism in the rat. The reduction of hepatic P450 produced by interferon may result from the suppression of multiple isozymes.

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.

Functional significance of amino acid residues within conserved hydrophilic regions in human interferons-alpha

Site-directed in vitro mutagenesis was used to create analogs of human interferons (IFNs)-alpha 1 and -alpha 4. Analogs were expressed in vitro using SP6 RNA polymerase and a rabbit reticulocyte lysate cell-free protein synthesis system. Amino acid substitutions for the highly conserved residues at positions 33, 121, 122 and 123 greatly reduced the antiviral and antiproliferative activities on human cells of IFNs-alpha 1 and -alpha 4. In general, the amino acid substitutions had much less effect on the antiviral activities on bovine, compared with human, cells. Substitutions at positions 31, 41, 42, 124, 134, 135 and 136 had little or no effect on the biological activities of the IFN analogs. The abrogation of antiviral activity resulting from amino acid substitutions for the arginine residue at position 33 suggests that this arginine residue is required for binding to the IFN-alpha receptor on the cell surface.

The cellular receptor of the alpha-beta interferons

This is a selective review of recent trends in research on the cellular receptor for the alpha-beta interferons. It deals mainly with work published in the last three years (1985-88), and therefore mainly with receptors for the human interferons. The binding characteristics of several human alpha interferons are examined, and the importance of in vitro experimental models for establishing the relationship between receptor binding and the cellular response is emphasized.

Electrostatic interactions in the cellular dynamics of the interferon-receptor complex

Using membrane preparations of the interferon receptor, prepared from cells of the Burkitt line, Daudi, we have examined the binding of three human recombinant alpha-interferons. 1. We discovered a binding titration of the interferons IFN-alpha A and IFN-alpha D in the pH range 6-9. Receptor binding, negligible at pH 6, rises to a maximum close to pH 9. We have shown that binding of IFN-alpha A at basic pH is to the same receptors as at neutrality and that IFN-receptor complexes extracted with digitonin are more stable at basic pH than they are at neutrality. 2. The recombinant interferon, IFN-alpha B, shows little change of binding in the pH range 6-9. At its basic optimum the binding of IFN-alpha A approaches that of IFN-alpha B, while at neutral pH the binding of IFN-alpha A is 3-4 times less. This difference at neutral pH is seen on intact cells as well as on membrane preparations. The specific activity of IFN-alpha B is close to that of IFN-alpha A, both of which are 10-20 times more active than IFN-alpha D; and the binding titration is, therefore, independent of the initial binding affinities. 3. Using hybrid IFNs constructed from the DNA sequences of alpha D and alpha B, we have isolated the sequence responsible for the binding titration to the segment comprising amino acids 61-92. Examination of these sequences reveals that Lys-84 is present in all the IFN-alpha except IFN-alpha B where it is replaced by Glu; and Tyr-90, present in most of the common IFN-alpha including alpha A and alpha D, is replaced by Asp in IFN-alpha B. Lys and Tyr would normally titrate in the pH range 6-9. We conclude that the binding titration is due to an electrostatic interaction and we propose that the interaction is between IFN-receptor complexes. The role of the interaction in the binding losses that accompany the antiproliferative effects of IFN is discussed.

Regulation of cell growth by interferon

Interferons can regulate growth and differentiation in a wide range of cell types. These mechanisms are currently being examined. Interferons inhibit the growth of tumour cells and are thus potential anti-cancer agents. They can also inhibit normal cell growth in vitro, and stimulate tumour cell growth in vitro. They may also be involved in some autoimmune diseases. This review examines the effect of interferons on cell proliferation, function, and growth, focusing primarily on in vitro cell systems.

Two domains in alpha interferons influence the efficacy of the antiviral response

Murine interferon-alpha 1 and murine interferon-alpha 4 share 80% of their amino acids, yet the proteins differ considerably in their ability to protect mouse or hamster cells against viral infection. With the aim of localizing areas within these proteins which influence the biological response we have constructed hybrid alpha 1 alpha 4 genes by means of homologous recombination of the parent genes. When the antiviral activities of these proteins were compared, it appeared that there are at least two domains that affect the biological response to these proteins: area A (amino acids 10-20) and area B (amino acids 55-67). These areas are presumably involved in the interaction between ligand and receptor. Most interestingly, hybrids in which area A from IFN-alpha 1 is combined with area B from alpha 4, have antiviral activities on homologous cells that are one to two orders of magnitude higher than those of the parent proteins.

Purification of human gamma interferon receptors by sequential affinity chromatography on immobilized monoclonal antireceptor antibodies and human gamma interferon

mAbs against human IFN-gamma (huIFN-gamma) receptors were obtained by immunizing a BALB/c mouse with eluates from immobilized recombinant huIFN-gamma (rhuIFN-gamma) on which lysates of enriched Raji cell membranes had been adsorbed. mAbs were selected for competitive inhibition of receptor binding of 125I-labeled rhuIFN-gamma. The following additional properties suggest that these antibodies are specific for huIFN-gamma receptors: they bind to the surface of human cells expressing IFN-gamma receptors but not to heterologous cells; this binding is inhibited competitively by addition of rhuIFN-gamma; the number of binding sites revealed by direct binding of 125I-labeled rhuIFN-gamma correlates with the amount of antigen recognized by the mAbs on different cell lines. A Triton X-100 extract of a membrane-enriched fraction of human Raji cells was affinity purified with these mAbs and the eluates from such columns were further purified on immobilized rhuIFN-gamma. As revealed by SDS-PAGE, the final eluate contained two major protein bands with approximate Mr of 90,000 (p90) and 50,000 (p50), respectively. Both proteins were able to specifically bind 125I-labeled rhuIFN-gamma upon electroblotting to nitrocellulose. This binding could be inhibited by the huIFN-gamma receptor mAbs, suggesting that the same epitopes are recognized on p90, p50, and on the cell surface. Therefore, these proteins most likely represent at least a part of huIFN-gamma receptors.

Single amino acid changes that render human IFN-alpha 2 biologically active on mouse cells

Human IFN-alpha 1 and IFN-alpha 2 differ in 28 of 166 amino acids and show very different specific antiviral activities on human and murine cells. We have identified, by hybrid scanning and site-directed mutagenesis, three residues in IFN-alpha 2, in positions 121, 125 and 132 which, when replaced individually or jointly by their IFN-alpha 1 counterparts, modify its activity on mouse cells by up to 400-fold. We argue that these residues are involved in direct contacts with the mouse interferon receptor.

Antiviral and antiproliferative activities of interferon-alpha 1: the role of cysteine residues

Site-specific in vitro mutagenesis was used to direct serine for cysteine substitutions within the sequence of human interferon-alpha 1 (IFN-alpha 1). Antiviral specific activities and antiproliferative activities of IFN-alpha 1 analogs, expressed in M13 as fusion proteins, were assessed following purification by monoclonal antibody affinity chromatography. Based on analysis of IFN-alpha 2, IFN-alpha 1 contains two disulfide bridges between cysteine residues 29 and 139 and cysteine residues 1 and 99. IFN-alpha 1 also contains a fifth cysteine residue at position 86. The series of serine for cysteine substitutions performed indicated that IFN-alpha 1 molecules unable to form the residue 29 to residue 139 disulfide bridge have substantially reduced antiviral and antiproliferative activities, IFN-alpha 1 molecules unable to form the residue 1 to residue 99 disulfide bridge have only marginally altered antiviral and antiproliferative activities, the low antiviral activity of IFN-alpha 1 compared with other human IFN-alpha subtypes is not due to the formation of nonnative disulfide bridges involving the fifth cysteine residue at position 86, which the other subtypes lack, and (iv) the reduced biological activities of certain analogs may be due to the formation of nonnative disulfide bridges.

Treatment with human recombinant leukocyte interferons inhibits in vitro invasive ability of human lung carcinoma cells

The effects of treatment of human lung carcinoma cell line A 549 with recombinant DNA-derived human leukocyte interferons A (rIFN-alpha A) or D (rIFN-alpha D), and human lymphoblastoid interferon (Wellferon) on in vitro cell invasion were investigated in a quantitative invasion assay using human amnion. The A 549 cells treated with IFN for one day were incubated on the denuded basement membrane of the amnion in the absence of IFN, and cells which penetrated the full thickness of the connective tissue barrier were measured after 4 days. A dose-dependent inhibition of cell invasion was produced by the recombinant IFNs. The one day treatment of cells with 2.4 X 10(3) to 1.8 X 10(4) units/ml of rIFN-alpha A resulted in a 60-80 per cent inhibition of invasiveness compared to untreated cells. After a one day exposure of cells to 2.2 X 10(4) units/ml of rIFN-alpha D, cell invasion was reduced by approximately 70 per cent; a concentration of 4.4 X 10(3) units/ml had no apparent effect. Similar treatment with lymphoblastoid IFN (6 X 10(4) units/ml) had no significant effect on cell invasion. Accompanying the one day exposure to rIFN-alpha A (1.8 X 10(4) units/ml) or rIFN-alpha D (2.2 X 10(4) units/ml), (2',5') oligo (A) synthetase activity was induced approximately 20-fold; a 4-fold induction of enzyme activity was found in cells exposed to lymphoblastoid IFN (6 X 10(4) units/ml). After exposure of A 549 cells to the three IFNs at these concentrations, no significant alteration of the ability of the cells to attach to the basement membrane was found. Moreover, none of the one day IFN treatment regimens were cytocidal, and cell proliferation ability was not affected. This model system may be useful for investigating anti-invasive activity of other IFN types and subtypes.

Transcriptional regulation of interferon-responsive genes is closely linked to interferon receptor occupancy

We show that human glioblastoma cells, moving from exponential growth into a state of density-dependent growth arrest, demonstrate a 7-fold drop in the total number of alpha-IFN-receptors expressed per cell. This loss of receptor activity was not seen when cells were grown in the presence of anti-alpha-IFN-monoclonal antibody. The active binding sites expressed on the arrested cell population were of reduced affinity for IFN, relative to the high-affinity sites expressed on the growing cells, resulting in a 3-fold lower initial rate of IFN-binding to the arrested cells. We exploited this difference to investigate the relationship between IFN receptor binding and induced gene transcription. As determined by nuclear run-off assays, the transcriptional response of both the gene family 1-8 and 2-5A synthetase to IFN treatment also showed a 3-fold reduction in density-arrested cells. Longer-term (0-8 h) induction and down-regulation of gene transcription in IFN-treated cells closely followed the binding to, and down-regulation of, cell surface-localized IFN receptors. Furthermore, inhibition of the intracellular breakdown of IFN did not affect transcriptional responses to IFN. Thus transcription of these IFN-induced genes is closely linked to surface receptor occupancy and is most likely mediated by transmembrane signals alone.

Differential human interferon alpha receptor expression on proliferating and non-proliferating cells

The expression of interferon-alpha (IFN-alpha) receptors was studied on a variety of human cells, using monoiodinated IFN-alpha 2 probes. Steady-state binding at 4 degrees C revealed a single class of non-interacting IFN receptor on peripheral blood lymphocytes, and tonsillar B lymphocytes, which are both known to be G0/G1 resting cell populations. The binding affinity of this class of receptor was found to be on the order of 5 X 10(-10) M, expressed as an apparent dissociation constant (Kd). However, cells proliferating either in culture or in vivo were found to express a heterogeneity in IFN-alpha 2 binding. Such binding could be objectively resolved (by a version of the LIGAND program of P. Munson) into a two-site receptor model. Hill plots of binding to proliferating cells indicated a negative cooperativity in the interaction of IFN and receptor. The high-affinity component, expressed on proliferating cells, typically exhibits a Kd of (1-10) X 10(-11) M, while the lower-affinity component indicates a Kd of (1-10) X 10(-9) M. Furthermore, the low-affinity component is apparently expressed on the order of 10-200 times the copy number, per cell, of the high-affinity site. Affinity-labeling experiments revealed that, in addition to the 140-160-kDa IFN-binding complex reported by others, both the proliferating and non-proliferating cell populations possess a novel IFN-binding component of 60 kDa.

Interferon effects on herpes simplex virus in rabbit and human cell cultures

The effects of four subtypes of recombinant human alpha interferon (RIFN alpha), (A,B,D, and the hybrid A/D) were tested on six strains of herpes simplex virus (HSV). RIFN alpha -D was the most effective subtype in rabbit kidney cells, which is consistent with our previous in vivo results in the rabbit herpetic keratitis model. In human corneal cells, however, RIFN alpha -D was one of the least effective IFN subtypes tested. Conversely, RIFN alpha-A appeared to be relatively more effective in the human corneal cells than in the rabbit kidney cells, but RIFN alpha -B and RIFN alpha -A/D were the most effective interferon subtypes in human corneal cells. Different strains of HSV had different susceptibilities to the various IFN subtypes tested.

Qualitative differences in effects of recombinant alpha-, beta- and gamma-interferons on human peripheral blood leukocytes in vitro

The in vitro effects of bacteria-produced human interferons alpha 2, beta and gamma on several properties of peripheral blood leukocytes from different healthy donors were compared. Treatment with HuIFN-alpha 2 or HuIFN-beta resulted in inhibition of the proliferative response to phytohaemagglutinin and in closely parallel induction of 2'-5'-oligoadenylate synthetase activity. In contrast, HuIFN-gamma had no significant effect on these two activities. However, all three HuIFN were able to enhance natural killer cell cytotoxicity and the expression of HLA-DR surface antigens, with only quantitative variations from donor to donor. Similar results were observed with glycosylated recombinant hamster-cell-derived HuIFN-gamma and with natural HuIFN-gamma. These data demonstrate qualitative differences in the effects of HuIFN-gamma compared to those of HuIFN-alpha 2 or -beta on cells of the immune system.

Alteration of some leukocyte functions following in vivo and in vitro exposure to recombinant bovine alpha- and gamma-interferon

Bovine interferons (BoIFNs) produced by recombinant DNA technology are currently being evaluated for their prophylactic effect against virus-induced respiratory disease in cattle. In this context experiments were conducted to compare blood levels of recombinant bovine interferon-alpha 1 (rBoIFN-alpha 1) and -gamma (rBoIFN-gamma) following intravenous and intramuscular injection to healthy calves, and to assess the effect on the immune response. Maximum serum level of IFN obtained with rBoIFN-gamma was less than 20% of that seen with rBoIFN-alpha 1 regardless of whether it was administered intravenously or intramuscularly. Nevertheless, administration of rBoIFN-gamma had a greater effect on leukocyte functions than rBoIFN-alpha 1, both with respect to level and duration of changes. Migration by polymorphonuclear neutrophils (PMN) became suppressed and their generation of O2- was enhanced following rBoIFN treatment. In vitro both rBoIFNs also suppressed migration, whereas the effect on O2- generation was minimal with suppression seen only at very high doses. Lymphocyte proliferation was also suppressed 24 h after IFN injection, and this effect could be reversed by exogenous interleukin-2 (IL-2) added to the cultures. In experiments designed to elucidate the mechanism of lymphocyte-suppression, it was found that in vitro treatment with rBoIFNs can induce suppressor cells, which may act by competing for IL-2. The combination of in vivo and in vitro experimental models used here could prove useful in additional studies to further delineate the mechanisms involved in the immunomodulatory effects of IFNs.

An interferon analogue, [Ala 30,32,33]HuIFN-alpha 2, acting as a HuIFN-alpha 2 antagonist on bovine cells

We have studied the biological and receptor binding properties of a human alpha 2-interferon (HuIFN-alpha 2) analogue, [Ala30,32,33] HuIFN-alpha 2, which is shown in the accompanying paper (1) to be biologically inactive on homologous cells. Here we demonstrate that this analogue is also devoid of biological activity on bovine MDBK cells. However, whereas the analogue did not inhibit the binding of radiolabeled HuIFN-alpha 2 to WISH cells, it did compete for binding to receptors on the bovine cells. This behavior suggested that [Ala30,32,33] HuIFN-alpha 2 could act as an antagonist of HuIFN-alpha 2 on bovine cells and indeed coaddition of the analogue and native HuIFN-alpha 2 to MDBK cells competitively inhibited both the antiviral and antiproliferative activity of HuIFN-alpha 2.

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.

Receptor dynamics of closely related ligands: "fast' and "slow' interferons

Two related human alpha interferons with 83% homology in their primary sequences show a similar specific activity on nonhuman cells, but a striking difference on human cells, on which alpha-1 shows 1-5% of the specific molar activity displayed by alpha-2. Both interferons were labelled with 125I, and their binding kinetics followed on growing cultures of the human Burkitt line Daudi. Binding of alpha-1 showed slower rates of association and faster rates of dissociation implying that differences in apparent binding affinity were responsible for the differences in specific molar activity. However, binding was shown to reach steady-state rather than an equilibrium, so differences in the dynamics of the ligand-receptor complexes may represent amplification of differences in the initial binding constant. alpha-2, but not alpha-1, induces a marked loss of binding sites leading to a high affinity steady-state binding. Inhibition of cell multiplication by both interferons depends on a continued stimulation by free ligands at steady-state. It is proposed that the differences in specific molar activity are, in the main, kinetic and cause alpha-1 and alpha-2 to behave respectively as "slow' and "fast' interferons.

Studies on cell binding and internalization of human lymphoblastoid (Namalva) interferon

The binding of iodinated human lymphoblastoid Namalva interferon to Namalva cells, to a human fibroblast cell strain (FS11), and to a bovine kidney cell line (MDBK) was characterized. Scatchard analysis of the binding data indicated the presence of about 1000-2000 receptors per cell and dissociation constants of the order of 0.1 to 0.01 nM. Two subspecies of Namalva interferon (16 K and 20 K), which differ in their antiviral activity toward bovine and human cells, were found to bind with the same affinity toward bovine MDBK cells but to differ in their affinity to human cells. Experimental results indicated that at 37 degrees C the bound interferon is internalized within 15 min after binding to Namalva cells, and then degraded in the lysosomes. Exposure of Namalva cells to interferon resulted in a 40% reduction of the number of cell surface receptors (down-regulation).

Receptors for human alpha and beta interferon but not for gamma interferon are specified by human chromosome 21

We examined the proposed role of human chromosome 21 in determining the cellular sensitivity to human alpha, beta, and gamma interferons (HuIFN-alpha, -beta, and -gamma) and the expression of the receptors for the HuIFNs with the use of mouse-human hybrid cells containing human chromosome 21. Hybrid cells (WA17) containing three copies of human chromosome 21 showed specific displaceable binding of 125I-labeled HuIFN-alpha 2 (125I-HuIFN-alpha 2), which was not observed with mouse parent (A9) cells. Crosslinking of 125I-HuIFN-alpha 2 bound to WA17 cells with disuccinimidyl suberate yielded a complex of Mr approximately equal to 150,000 similar to the 125I-HuIFN-alpha 2-receptor complex obtained with human cells as described earlier. Such a complex was not obtained with mouse parent (A9) cells or with hybrid cells containing certain other human chromosomes but not chromosome 21. Mice inoculated with mouse-human hybrid cells containing human chromosome 21 produce antibodies that block the antiviral action of HuIFN-alpha and -beta on human cells. Such antibodies could immunoprecipitate the 125I-HuIFN-alpha 2-receptor complex obtained from human cells but not free 125I-HuIFN-alpha 2, indicating that these antibodies were directed against the receptor. WA17 hybrid cells were highly sensitive to the antiviral action of HuIFN-alpha 2, -alpha (Le) and -beta but were completely insensitive to HuIFN-gamma. Furthermore, 125I-HuIFN-gamma showed specific binding to human WISH cells but not to WA17 hybrid cells or A9 mouse cells. The results indicate that the receptors for HuIFN-alpha and -beta but not for HuIFN-gamma are specified by human chromosome 21. Hybrid cells containing one, two, or three copies of human chromosome 21 were found to be increasingly sensitive to HuIFN-alpha 2, indicating that a chromosome 21-specified component (possibly the HuIFN-alpha receptor) may be a limiting factor in the cellular sensitivity to HuIFN-alpha.

Receptor mediated pathways for interferon action: in vivo implications

High affinity receptors for human interferon (IFN) are a common surface component of human nucleated cells. A model culture system has been used to mark the activation of surface receptors by IFN as the first step in several, possibly separate, pathways of action, some of which depend on the continued presence of IFN. Two types of equilibrium binding can be seen: an initial one of short duration corresponding to receptor activation and a second of longer duration corresponding to activation of a second site by IFN. Various different responses to IFN are seen to be determined by one or other of these equilibria. In vivo, implications are discussed in terms of the pharmacokinetic distribution of IFN, with particular reference to intravenous injection. Desensitization of target cells with respect to late equilibrium effects is seen as a possible consequence of receptor activation against the background of changing IFN concentration in vivo. A modulating effect of combined IFN species is proposed.