Time course of interferon levels, antiviral state, 2',5'-oligoadenylate synthetase and side effects in healthy men

Antiviral activity of the interferon α family: biological and pharmacological aspects of the treatment of chronic hepatitis C

INTRODUCTION

Type I interferons (IFNs) comprise a group of at least 13 structurally related subtypes of IFN-α with similar, but not identical, biological activities. Each subtype displays a unique activity profile; only IFN-α2a and IFN-α2b subtypes together with natural IFN-α preparations are currently used in the clinical practice, so that the remaining IFN-α subtypes are a still unexploited reservoir of opportunity also in the new era of direct-acting antiviral agents for the treatment of hepatitis C virus (HCV).

AREAS COVERED

This paper reviews recent progress in the study of the biology of IFN family, the antiviral action mechanism and the strategies employed by HCV to evade IFN action. Currently available IFN preparations for the treatment of chronic hepatitis C infection are described and what is currently known on the pharmacokinetics, pharmacodynamics and immunogenicity of IFN-α preparations used in clinical practice are summarized.

EXPERT OPINION

The characterization of multifunctional nature of IFN system together with recent advances in the identification of HCV IFN evasion strategies and the variety of host factors influencing IFN treatment response should be considered to improve HCV and other infectious diseases treatment in the future.

Alpha interferon induces long-lasting refractoriness of JAK-STAT signaling in the mouse liver through induction of USP18/UBP43

Recombinant alpha interferon (IFN-alpha) is used for the treatment of viral hepatitis and some forms of cancer. During these therapies IFN-alpha is injected once daily or every second day for several months. Recently, the long-acting pegylated IFN-alpha (pegIFN-alpha) has replaced standard IFN-alpha in therapies of chronic hepatitis C because it is more effective, supposedly by inducing a long-lasting activation of IFN signaling pathways. IFN signaling in cultured cells, however, becomes refractory within hours, and little is known about the pharmacodynamic effects of continuously high IFN-alpha serum concentrations. To investigate the behavior of the IFN system in vivo, we repeatedly injected mice with IFN-alpha and analyzed its effects in the liver. Within hours after the first injection, IFN-alpha signaling became refractory to further stimulation. The negative regulator SOCS1 was rapidly upregulated and likely responsible for early termination of IFN-alpha signaling. For long-lasting refractoriness, neither SOCS1 nor SOCS3 were instrumental. Instead, we identified the inhibitor USP18/UBP43 as the key mediator. Our results indicate that the current therapeutic practice using long-lasting pegIFN-alpha is not well adapted to the intrinsic properties of the IFN system. Targeting USP18 expression may allow to exploit the full therapeutic potential of recombinant IFN-alpha.

Peginterferon α-2b in the treatment of hepatitis C

Hepatitis C virus (HCV) is a leading public health problem affecting as many as 4 million Americans. Chronic HCV infection can progress to hepatocellular carcinoma, cirrhosis and death. Interferon-α-based therapies, initially as monotherapy and later in combination with ribavirin, have proven effective in the treatment of HCV infection, but standard interferon is hampered pharmacokinetically by a short half life. With the advent of the pegylated-interferons, administered in combination with oral ribavirin, the chances for HCV eradication have improved further. Peginterferon α-2b, the formuation discussed in this review, provides greater antiviral pressure while maintaining a tolerable side-effect profile with more convenient once-weekly dosing. Clinical trials have focused on treatment-naïve patients as well as on many different HCV subpopulations, including difficult-to-treat patients such as previous interferon therapy failures and patients with HCV cirrhosis.

Antiviral therapies in children: has their time arrived?

The increase in the number and classes of antiviral agents that has occurred since the 1980s is remarkable. The rapid expansion in therapeutic options for previously untreatable illnesses challenges clinicians to gain familiarity and experience with these new drugs, especially with regard to their use in children. This article describes the clinical utilities, pharmacokinetics, and adverse effects of these new drugs to empower practitioners to use them appropriately.

Structural and Biophysical Characterization of the 40 kDa PEG−Interferon-α2aand Its Individual Positional Isomers

The human recombinant Interferon-alpha(2a) (IFNalpha(2a)) is a potent drug (Roferon-A) to treat various types of cancer and viral diseases including Hepatitis B/C infections. To improve the pharmacological properties of the drug, a new pegylated form of IFNalpha(2a) was developed (PEGASYS). This 40 kDa PEG-conjugated IFNalpha(2a) ((40)PEG-IFNalpha(2a)) is obtained by the covalent binding of one 40 kDa branched PEG-polymer to a lysine side chain of IFNalpha(2a). (40)PEG-IFNalpha(2a) is a mixture of mainly six monopegylated positional isomers modified at K31, K134, K131, K121, K164, and K70, respectively. Here we report the detailed structural and biophysical characterization of (40)PEG-IFNalpha(2a) and its positional isomers, in comparison with IFNalpha(2a), using NMR spectroscopy, analytical ultracentrifugation, circular dichroism, fluorescence spectroscopy, and differential scanning calorimetry. Our results show that the three-dimensional structure of IFNalpha(2a) is not modified by the presence of the polymer in all positional isomers constituting (40)PEG-IFNalpha(2a). Regardless of where the PEG-polymer is attached, it adopts a very mobile and flexible random coil conformation, producing a shield for the protein without a permanent coverage of the protein surface. Hydrodynamic data indicate that the protein-attached PEG has a slightly more compact random-coil structure than the free PEG-polymer. Our results also provide evidence of significant structural and physicochemical advantages conferred by the pegylation: increase of the effective hydrodynamic volume and modification of the molecular shape, higher temperature stability, and reduced tendency for aggregation. These results are of tremendous pharmacological interest and benefit as was clinically shown with PEGASYS. This study constitutes a new standard for the characterization of pegylated proteins and enables an important step toward the understanding on a molecular level of the binding of (40)PEG-IFNalpha(2a) and its positional isomers to its cellular receptors.

Regulation of Gene Expression by Pegylated IFN-α2b and IFN-α2b in Human Peripheral Blood Mononuclear Cells

The pleiotropic biologic effects of interferon (IFN) are mediated through regulation of the expression of numerous IFN-sensitive genes. Peripheral blood mononuclear cells (PBMCs) obtained from healthy donors were analyzed to study the immunoregulatory and antiviral messenger RNAs (mRNAs) and proteins regulated by pegylated IFN-alpha2b (PEG-IFN-alpha2b) and IFN-alpha2b. A dose-dependent and time-dependent response for multiple IFN-regulated genes was observed. IFN-dependent protein production and secretion were correlated with IFN-regulated mRNA induction. Overall regulation of gene expression patterns for PEG-IFN-alpha2b and IFN-alpha2b was comparable, even though the antiviral activity of PEG-IFN-alpha2b demonstrated a longer biologic halflife in vitro compared with IFN-alpha2b. To study the heterogeneity of responses, PBMCs obtained from over 25 healthy donors were analyzed. Within a particular donor dataset, gene-specific and dose-dependent responses to PEG-IFN-alpha2b treatment, demonstrated in both the amplitude of transcriptional upregulation and the duration of sustained mRNA upregulation, were observed. However because of donor heterogeneity, the amplitude of a given transcriptional response could not be predicted for a specific dose of PEG-IFN-alpha2b. Notably, mRNA levels of oligoadenylate synthetase (OAS), double-stranded RNA (dsRNA)-activated protein kinase (PKR), IP-10, IFN-stimulated gene 54 (ISG54), and ISG15 were upregulated after 120 h of continuous PEG-IFN-alpha2b treatment. These results suggest that the use of antiviral and immunoregulatory protein mRNA levels as markers to assess the therapeutic efficacy of IFN-alpha2b and PEG-IFN-alpha2b against viral and neoplastic diseases in clinical trials is promising but will require further analysis using clinical patient samples.

A prospective comparison of the effect of interferon-alpha and interferon-beta treatment in patients with chronic hepatitis C on the incidence of hepatocellular carcinoma development

To investigate differences in the effect of interferon (IFN) -alpha and IFN-beta treatment for hepatitis C on hepatocellular carcinoma (HCC) development, we prospectively followed 351 consecutive patients (median age, 56.6 years; mean follow-up, 5.7 +/- 2.6 years) with chronic hepatitis C virus (HCV) viremia. Of 260 IFN-alpha and 91 IFN-beta treated patients, 17 (6.5%) and 4 (4.4%), respectively, developed HCC. Virological response (VR) was defined as persistent HCV RNA disappearance from serum, and biochemical response (BR) as persistent alanine aminotransferase (ALT) normalization after treatment. No significant between-group differences in HCC development were found between those with and without VR. Although the HCC development rate in patients without BR was significantly higher than that in patients with BR in the IFN-alpha group (11.4% and 0.8%; P << 0.05), no significant difference was found in the IFN-beta group (6.3% and 2.3%). Similar rates of HCC development were found in patients with chronic HCV viremia treated with either IFN-alpha or IFN-beta.

Isolation, structural characterization, and antiviral activity of positional isomers of monopegylated interferon alpha-2a (PEGASYS)

Interferon alpha-2a plays an essential role in the treatment of chronic hepatitis C, but it is limited in its efficacy by the short in vivo half-life. To improve the half-life and efficacy, interferon alpha-2a is conjugated with a 40-kDa branched polyethylene glycol moiety (PEG-IFN, PEGASYS). From this preparation the positional PEG-IFN isomers were isolated and characterized by different analytical methods and antiviral assay. Two chromatographic steps were used to separate and purify nine isomers. The analytical methods IE-HPLC, RP-HPLC, SE-HPLC, SDS-PAGE, and MALDI-TOF MS indicated that each of these nine isomers is conjugated to the branched polyethylene glycol chain at a specific lysine. No isomer with a modification at the amino terminus was observed. All positional isomers induced viral protection of MDBK cells in the antiviral assay. When comparing the quantitative potency of the individual isomers with the whole mixture of PEG-IFN, significant differences in the specific activities were observed: PEG-Lys(31) and PEG-Lys(134) showed higher activities than the mixture, PEG-Lys(164) was equal to the mixture, whereas the activities of PEG-Lys(49), PEG-Lys(70), PEG-Lys(83), PEG-Lys(112), PEG-Lys(121), and PEG-Lys(131) were lower.

Pegylated interferons for the treatment of chronic hepatitis C infection

BACKGROUND

Interferon (IFN) alfa is a clinically effective therapy used in a wide range of viral infections and cell-proliferative disorders. Combination therapy with IFN alfa-2b and ribavirin is the current standard of care for the treatment of chronic hepatitis C (CHC) infection. However, standard IFN alfa has the drawbacks of a short serum half-life and rapid clearance. To overcome this problem, 2 pegylated forms of IFN have been developed and tested clinically.

OBJECTIVE

This article reviews the development and properties of pegylated IFN alfa-2b and pegylated IFN alfa-2a, and presents safety and efficacy data from recent clinical trials.

METHODS

Relevant clinical studies were identified through a MEDLINE search from 1966 through the present using the key words hepatitis C and interferon. Studies of the pegylated IFNs in humans were then selected.

RESULTS

Pegylated IFN alfa-2b is formed by covalent conjugation of a 12-kd mono-methoxy polyethylene glycol (PEG) molecule to IFN alfa-2b, and pegylated IFN alfa-2a by covalent conjugation of a 40-kd branched mono-methoxy PEG molecule to IFN alfa-2a. The 2 pegylated IFNs differ in the mixture of pegylation isomers resulting from their conjugation chemistry. Pegylated IFN alfa-2b has a prolonged serum half-life (40 hours) relative to standard IFN alfa-2b (7-9 hours). The greater polymer size of pegylated IFN alfa-2a acts to reduce glomerular filtration, markedly prolonging its serum half-life (72-96 hours) compared with standard IFN alfa-2a (6-9 hours). In clinical studies, once-weekly dosing of the pegylated IFNs was associated with a sustained virologic response in patients infected with hepatitis C virus (HCV). Once-weekly dosing with either of the pegylated IFNs was more effective than the respective thrice-weekly regimen of IFN alfa, with a comparable safety profile. The combination of once-weekly pegylated IFN and ribavirin effectively reduced HCV viral load and sustained viral suppression.

CONCLUSIONS

Once-weekly dosing with either pegylated IFN alfa-2b or pegylated IFN alfa-2a has been shown to produce significantly higher rates of viral eradication than standard thrice-weekly IFN alfa therapy without compromising safety. With respect to the treatment of CHC, the greatest anti-HCV efficacy has been achieved with the combination of once-weekly pegylated IFN and ribavirin.

Peginterferon alfa-2a (40 kDa) monotherapy: a novel agent for chronic hepatitis C therapy

Current therapy for hepatitis C remains far from optimal. The modification of IFN by the attachment of a polyethylene glycol (PEG) moiety has produced long-lasting IFNs. A 40 kDa branched peginterferon alfa-2a (40 kDa) (PEG-IFN alfa-2a) has unique pharmacokinetic and pharmacodynamic properties. PEG-IFN alfa-2a is absorbed in a sustained manner and its clearance is reduced substantially compared with IFN alfa-2a, resulting in sustained serum drug concentrations. These constant serum drug levels stay above the EC(50) values (effective concentration 50%) needed for antiviral, antiproliferative and immunomodulatory actions. Sustained virological responses were significantly greater in patients who received PEG-IFN alfa-2a versus IFN alfa-2a, with a similar side effect profile. Histological improvements were seen in patients who achieved sustained virological responses and were frequently observed among patients who did not achieve a virological response. The advantages of PEG-IFN alfa-2a were also seen in patients with cirrhosis or hepatitis C virus (HCV) genotype 1.

The kinetics of hepatitis C virus infection

Mathematical modeling of viral dynamics reveals high turnover rates of pretreatment viral production and clearance (10(11)-10(13) virions/day) and permits the estimation of in-vivo half-lives of a few hours for HCV free virions. The balance between virus production and clearance in untreated patients with chronic hepatitis C virus results in a decline of viremia when active antiviral treatment is initiated. During the first phase of IFN-alpha therapy, the kinetics of the viral load is characterized by a rapid, dose-dependent decline. After about 24 to 48 hours, the viral decline enters a second phase of a relatively slow exponential decay during the following weeks of therapy which may reflect the death rate of infected hepatocytes. The second-phase decay is predictive for the virologic end-of-treatment status and, even more so, for the likelihood of sustained response. Nonresponding patients typically show constant viremia or even a rebound during this second phase.

Viral kinetics in patients with chronic hepatitis C treated with standard or peginterferon alpha2a

BACKGROUND & AIMS

Covalent attachment of a 40-kilodalton polyethylene glycol moiety to interferon alpha2a (peginterferon alpha2a) results in sustained delivery and reduced clearance compared with standard interferon alpha2a. The aim of the study was to compare viral kinetics in patients treated with standard or peginterferon alpha2a.

METHODS

Patients with chronic hepatitis C were randomly assigned to receive either standard interferon alpha2a thrice weekly (n = 16) or 180 microg peginterferon alpha2a once weekly (n = 17) for 48 weeks. HCV RNA was quantitated before and frequently during treatment.

RESULTS

The extent of the second-phase decline of HCV RNA, representing the degradation rate of infected cells during therapy for responding patients, was 0.02 +/- 0.03 day(-1) (HCV-1), 0.88 +/- 0.64 day(-1) (HCV non-1), 0.06 +/- 0.08 day(-1) (HCV-1), and 0.44 +/- 0.33 day(-1) (HCV non-1) in patients treated with standard or peginterferon alpha2a, respectively. The second-phase decline was low (<0.05 day(-1)) in most patients without a virological end-of-treatment response, and the second-phase decline was high (>0.25 day(-1)) in all patients with sustained virological response.

CONCLUSIONS

The degradation rate of infected cells is HCV genotype dependent. Treatment with peginterferon alpha2a may reinforce the death rate of infected cells (particularly in HCV-1-infected patients) or stabilize the therapeutic effect on viral production. The second-phase decline of HCV RNA is predictive of virological sustained response.

Rational design of a potent, long-lasting form of interferon: a 40 kDa branched polyethylene glycol-conjugated interferon alpha-2a for the treatment of hepatitis C

A potent, long-lasting form of interferon alpha-2a mono-pegylated with a 40 kilodalton branched poly(ethylene glycol) was designed, synthesized, and characterized. Mono-pegylated interferon alpha-2a was comprised of four major positional isomers involving Lys31, Lys121, Lys131, and Lys134 of interferon. The in vitro anti-viral activity of pegylated interferon alpha-2a was found to be only 7% of the original activity. In contrast, the in vivo antitumor activity was severalfold enhanced compared to interferon alpha-2a. Pegylated interferon alpha-2a showed no immunogenicity in mice. After subcutaneous injection of pegylated interferon alpha-2a, a 70-fold increase in serum half-life and a 50-fold increase in mean plasma residence time concomitant with sustained serum concentrations were observed relative to interferon alpha-2a. These preclinical results suggest a significantly enhanced human pharmacological profile for pegylated interferon alpha-2a. Results of Phase II/III hepatitis C clinical trials in humans confirmed the superior efficacy of pegylated interferon alpha-2a compared to unmodified interferon alpha-2a.

Use of an indirect pharmacodynamic stimulation model of MX protein induction to compare in vivo activity of interferon alfa-2a and a polyethylene glycol-modified derivative in healthy subjects

Interferon alfa-2a was chemically modified by the covalent attachment of a polyethylene glycol (PEG) moiety to enhance its circulating half-life and to reduce its immunogenicity. A comparative evaluation of the pharmacokinetics of the PEG-modified interferon alfa-2a showed a greater than twofold increase in the circulating half-life as a result of this chemical modification. An indirect physiologic response model was developed to characterize the time course of the MX protein response after subcutaneous administration of single ascending doses of either interferon alfa-2a or PEG-interferon alfa-2a in healthy volunteers. Analysis of the pharmacokinetic-pharmacodynamic relationship suggested that the PEG-modified interferon alfa-2a could not be administered less than twice weekly and therefore offered little therapeutic advantage over its unmodified counterpart, which is administered three times weekly. These results were consistent with findings in phase II trials. This study substantiates the usefulness of pharmacodynamic modeling as a tool for the development of dose recommendations and for the early selection of drug candidates in the drug development process.

Effect of alpha interferon (IFN-alpha) on 2'-5' oligoadenylate synthetase activity in peripheral blood mononuclear cells of patients with chronic hepatitis C: relationship to the antiviral effect of IFN-alpha

Alpha interferon (IFN-alpha) is, to date, the only treatment with proven efficacy in patients with chronic hepatitis C. However, less than 15% of the patients have a sustained response to IFN-alpha. Interferon acts through the induction of various cellular enzymes. Among them, the 2'-5' oligoadenylate synthetase (2-5OAS) is (at least in part) responsible for a direct antiviral effect of IFN-alpha. The aim of this study was to determine whether basal and IFN-alpha-induced in vivo and in vitro 2-5OAS activities measured in peripheral blood mononuclear cells predict biochemical and virological responses to IFN-alpha in patients with chronic hepatitis C. 2-5OAS activity in peripheral blood mononuclear cells and the antiviral effect of IFN-alpha were studied in 36 patients with chronic hepatitis C (27 men and 9 women; mean age, 44.7 years). Basal in vivo 2-5OAS activity (mean +/- standard error of the mean) was 4.41 +/- 0.69 nmol/10(6) cells. It was significantly induced at month 3 of IFN-alpha therapy (18.07 +/- 2.74 nmol/10(6) cells; P = 0.0001). No significant differences were found in basal in vivo 2-5OAS activities, in IFN-alpha-induced/basal in vitro 2-5OAS activity ratios, in IFN-alpha-induced in vivo 2-5OAS activities, and in IFN-alpha-induced/basal in vivo 2-5OAS activity ratios between the patients with and without a biochemical response (normal alanine aminotransferase activity in serum) or a virological response (normal alanine aminotransferase activity in serum and negative hepatitis C virus RNA detection) at any step of the study. At month 3 of therapy, p69, which is considered to be the active isoform of 2-5OAS, was induced, as demonstrated by Western blot (immunoblot) analysis in 50% of the patients, and induction of the p100 isoform was observed in 70% of the patients. No significant relationship with the response to IFN-alpha therapy was observed. Our results suggest that a deficiency of the IFN-alpha-dependent 2-5OAS system, which could be genetically determined, is unlikely to be responsible for the failure to achieve biochemical and virological responses to IFN-alpha therapy in patients with chronic hepatitis C.

Modulation of alpha-interferon's antiviral and clinical effects by aspirin, acetaminophen, and prednisone in healthy volunteers

The magnitude and duration of the antiviral and clinical effect of alpha-interferon was measured in healthy volunteers. A single 3 million unit intramuscular dose of interferon was given either alone (controls) or after 72 h of concomitant medications. These medications included either aspirin (650 mg every 4 h), acetaminophen (650 mg every 4 h), or prednisone (40 mg per day). Peripheral blood mononuclear cells were assayed for resistance to vesicular stomatitis virus infection and induction of 2'-5'-oligoadenylate synthetase activity as evidence of interferon's antiviral effect. Co-administration of acetaminophen increased both antiviral parameters by more than 70% (P < 0.05) and reduced symptoms after interferon dosing, compared to controls. Aspirin and prednisone did not demonstrate any significant differences from controls in antiviral effect. As a group, acetaminophen, aspirin, and prednisone reduced the clinical symptoms by 47% compared to controls (P = 0.03) after interferon dosing, although individual drug comparisons failed to reach statistical significance. Independent of treatment group, the changes in antiviral markers after interferon dosing correlated closely with each other (r = 0.72, P < 0.001), but neither correlated with symptoms or fever (r < 0.30, P > 0.05). Acetaminophen enhances the antiviral effects of a single intramuscular dose of alpha-interferon, considering the parameters measured in these healthy volunteers.

Activity of the interferon-induced 2',5'-oligoadenylate synthetase in patients with chronic hepatitis C

The interferon-induced 2',5'-oligoadenylate synthetase (2-5OAS) is responsible, at least in part, for the antiviral state established in cells in response to viral infections. The purpose of this work was to study the relationship between hepatitis C virus (HCV) infection and 2-5OAS in patients with chronic hepatitis C. Peripheral blood mononuclear cells (PBMC) of 27 patients with chronic hepatitis C were investigated, as well as PBMC of 10 control subjects. Then, the patients were treated with 3 mu interferon-alpha 2a three times per week. At month 3 of therapy, PBMC were sampled. Of the total PBMC samples obtained, half were used for determination of in vivo 2-5OAS activity. The remaining cells were cultured for 24 h in either the absence or presence of 500 U/ml of interferon-alpha 2a for the determination of in vitro 2-5OAS activity. The mean basal in vivo 2-5OAS activities were 3.6 +/- 2.8 nmol/10(6) cells in patients versus 1.6 +/- 1.1 nmol/10(6) cells in controls (p < 0.01). Basal in vivo 2-5OAS activity did not correlate with mean HCV viremia, quantified by a "branched DNA"-based assay. Before treatment, interferon-alpha was detected in the serum of 2 patients in 27. After a 24 h culture of PBMC in the presence of interferon, in vitro 2-5OAS activity was significantly induced in the PBMC of both the patients and the controls. However, in vitro induction of 2-5OAS activity was significantly lower in the PBMC of the patients than in the PBMC of the controls (p < 0.01). At month 3 therapy, in vivo 2-5OAS activity was significantly induced (20.5 +/- 17.9; p < 0.0001). In vitro IFN inductions of 2-5OAS activity in PBMC before treatment and at month 3 of therapy were not significantly different. In conclusion, in vivo 2-5OAS activity is significantly induced in patients with chronic hepatitis C, but endogenously produced interferon-alpha does not seem to be involved. Chronic induction of 2-5OAS activity results in a decreased sensitivity of PBMC to exogenous interferon induction. Whether this phenomenon plays a role in the resistance of chronic hepatitis C to interferon therapy remains uncertain.

Hormonal and immunological regulation of 2', 5'-oligoadenylate synthetase activity in human peripheral blood mononuclear cells

A newly developed method for assaying 2', 5'-oligoadenylate (2, 5A) synthetase activity by polyacrylamide gel electrophoresis was applied to peripheral blood mononuclear cells (PBMC) from normal subjects, HIV-positive subjects, and renal cell carcinoma (RCC) patients. Sex differences were observed in 2, 5A synthetase activity of PBMC from normal young adults, males having eightfold higher activities of this enzyme than females. Moreover, compared to values for postmenopausal (PM) females receiving estrogen replacement, untreated PM females had higher activities. Collectively, these results suggest that estrogen downregulates 2, 5A synthetase activity. Activities of 2, 5A synthetase were investigated in two disease states associated with altered immune function. In one patient with AIDS-related Kaposi's sarcoma, interferon-alpha (IFN-alpha) therapy increased 2, 5A synthetase activity twofold. In addition, combined therapy with interleukin-2 (IL-2) and IFN-alpha increased 2, 5A synthetase activities in eight of nine patients with RCC. Therefore, in patients receiving immunotherapy with IL-2 and IFN-alpha, our new assay could contribute to evaluation of immune stimulation. In general, studies in vitro confirmed these observations; however, exposure of PBMC from RCC patients revealed that in vitro IL-2 failed to induce this enzyme activity as it did in PBMC from normal volunteers.

Induction of Mx-related protein in cat peripheral blood mononuclear cells after administration of recombinant human interferon hybrid

A 78 kDa protein was induced in cat peripheral blood mononuclear cells after in vivo administration of recombinant human interferon-alpha hybrid (rHuIFN-alpha B/D). This protein was antigenically related to the IFN-induced human (78 kDa) and mouse Mx proteins. Quantitative immunoblot analysis indicated that the induction of the cat Mx protein was dose-dependent. There was a dissociation in time between plasma levels of IFN which were transient, and levels of cat Mx protein which remained elevated at least five days after dosing. Our results provide evidence that a human IFN-alpha hybrid may be active in cats. They also indicate that the Mx protein is a sensitive, quantitative, and stable marker to follow IFN activity in vivo in cats.

2',5' oligoadenylate synthetase activity in bovine peripheral blood mononuclear cells following bovine herpesvirus type-1-induced respiratory disease: a prognostic indicator?

Following aerosol-challenge of nonimmune calves with bovine herpesvirus type-1 (BHV-1) the levels of 2',5' oligoadenylate (2-5A) synthetase in peripheral blood mononuclear cells (PBML) increased significantly to peak 4-5 days after BHV-1 infection. This corresponded temporally to the period of highest susceptibility to secondary bacterial infection. Ten days post virus infection, the enzyme levels had returned to baseline values. Aerosol challenge with bacteria (Pasteurella haemolytica) did not induce 2-5A synthetase activity in PBML, neither did it influence the kinetics of 2-5A synthetase induction by virus infection during a dual viral-bacterial infection. Pretreatment of animals with bovine recombinant interferons (IFNs) 0-96 h prior to virus challenge curtailed the viral infection and thus reduced the levels of 2-5A synthetase induced by endogenously produced IFN. A relationship between 2-5A synthetase levels on day 5 post virus infection and clinical outcome of the dual infection was noted. Moreover, the high 2-5A synthetase levels could be correlated with low plasma Zn levels, another indicator of clinical respiratory disease. These results indicate that these two parameters, 2-5A synthetase and plasma Zn, in combination have potential prognostic value in viral-bacterial infections of the respiratory tract.

Recombinant interferons alpha and gamma: comparative antiviral activity and synergistic interaction in encephalomyocarditis virus infection of mice

The antiviral properties of 2 recombinant DNA-produced interferons, a human hybrid interferon alpha that is active in mice and a murine interferon gamma, were examined in the treatment of mice infected with encephalomyocarditis virus. A single dose of interferon alpha induced a protective state in mice more rapidly than did interferon gamma, but the activity of the latter was more long lasting. When interferon and virus were administered 6 h apart, either intraperitoneally or intravenously, interferons alpha and gamma were equally effective. However, this was not the case when the routes of treatment and infection were different. Interferon alpha showed somewhat reduced activity when the route of administration (intravenous) was different from the route of virus challenge (intraperitoneal) while interferon gamma showed very little activity when tested in this manner. When interferons alpha and gamma were administered in combination to mice, a marked synergistic antiviral effect was observed.