Interferon receptors

cART Restores Transient Responsiveness to IFN Type 1 in HIV-Infected Humanized Mice

The lack of a human immunodeficiency virus (HIV) cure has heightened interest in immunotherapy. As such, type I interferons (IFNs), in particular, IFN alpha (IFN-α), have gained renewed attention. However, HIV pathogenesis is driven by sustained IFN-mediated immune activation, and the use of IFNs is rather controversial. The following questions therein remain: (i) which IFN-α subtype to use, (ii) at which regimen, and (iii) at what time point in HIV infection it might be beneficial. Here, we used IFN-α14 modified by PASylation for its long half-life in vivo to eventually treat HIV infection. We defined the IFN dosing regimen based on the maximum increase in interferon-stimulated gene (ISG) expression 6 h after its administration and a return to baseline of ubiquitin-specific protease 18 (USP18) prior to the next dose. Notably, USP18 is the major negative regulator of type I IFN signaling. HIV infection resulted in increased ISG expression levels in humanized mice. Intriguingly, high baseline ISG levels correlated with lower HIV load. No effect was observed on HIV replication when PASylated IFN-α14 was administered in the chronic phase. However, combined antiretroviral therapy (cART) restored responsiveness to IFN, and PASylated IFN-α14 administered during analytical cART interruption resulted in a transiently lower HIV burden than in the mock-treated mice. In conclusion, cART-mediated HIV suppression restored transient IFN responsiveness and provided a potential window for immunoenhancing therapies in the context of analytical cART interruption. IMPORTANCE cART is highly efficient in suppressing HIV replication in HIV-infected patients and has resulted in a dramatic reduction in morbidity and mortality in HIV-infected people, yet it does not cure HIV infection. In addition, cART has several disadvantages. Thus, the HIV research community is exploring novel ways to control HIV infection for longer periods without cART. Here, we explored novel, long-acting IFN-α14 for its efficacy to control HIV replication in HIV-infected humanized mice. We found that IFN-α14 had no effect on chronic HIV infection. However, when mice were treated first with cART, we observed a transiently restored responsiveness to INF and a transiently lower HIV burden after stopping cART. These data emphasize (i) the value of cART-mediated HIV suppression and immune reconstitution in creating a window of opportunity for exploring novel immunotherapies, (ii) the potential of IFNs for constraining HIV, and (iii) the value of humanized mice for exploring novel immunotherapies.

Interferon Receptor Trafficking and Signaling: Journey to the Cross Roads

Like most plasma membrane proteins, type I interferon (IFN) receptor (IFNAR) traffics from the outer surface to the inner compartments of the cell. Long considered as a passive means to simply control subunits availability at the plasma membrane, an array of new evidence establishes IFNAR endocytosis as an active contributor to the regulation of signal transduction triggered by IFN binding to IFNAR. During its complex journey initiated at the plasma membrane, the internalized IFNAR complex, i.e. IFNAR1 and IFNAR2 subunits, will experience post-translational modifications and recruit specific effectors. These finely tuned interactions will determine not only IFNAR subunits destiny (lysosomal degradation vs. plasma membrane recycling) but also the control of IFN-induced signal transduction. Finally, the IFNAR system perfectly illustrates the paradigm of the crosstalk between membrane trafficking and intracellular signaling. Investigating the complexity of IFN receptor intracellular routes is therefore necessary to reveal new insight into the role of IFNAR membrane dynamics in type I IFNs signaling selectivity and biological activity.

Flagellin-Stimulated Production of Interferon-β Promotes Anti-Flagellin IgG2c and IgA Responses

Flagellin, a major structural protein of the flagellum found in all motile bacteria, activates the TLR5- or NLRC4 inflammasomedependent signaling pathway to induce innate immune responses. Flagellin can also serve as a specific antigen for the adaptive immune system and stimulate anti-flagellin antibody responses. Failure to recognize commensal-derived flagellin in TLR5-deficient mice leads to the reduction in antiflagellin IgA antibodies at steady state and causes microbial dysbiosis and mucosal barrier breach by flagellated bacteria to promote chronic intestinal inflammation. Despite the important role of anti-flagellin antibodies in maintaining the intestinal homeostasis, regulatory mechanisms underlying the flagellin-specific antibody responses are not well understood. In this study, we show that flagellin induces interferon-β (IFN-β) production and subsequently activates type I IFN receptor signaling in a TLR5- and MyD88-dependent manner in vitro and in vivo . Internalization of TLR5 from the plasma membrane to the acidic environment of endolysosomes was required for the production of IFN-β, but not for other proinflammatory cytokines. In addition, we found that antiflagellin IgG2c and IgA responses were severely impaired in interferon-alpha receptor 1 (IFNAR1)-deficient mice, suggesting that IFN-β produced by the flagellin stimulation regulates anti-flagellin antibody class switching. Our findings shed a new light on the regulation of flagellin-mediated immune activation and may help find new strategies to promote the intestinal health and develop mucosal vaccines.

The Cytokine Network: Their Role in Physiopathology and Therapeutic Implications

Lymphocytes, accessory-endothelial-and inflammatory-cells produce a variety of soluble factors termed cytokines. These are regulatory molecules which appear after the immune response at all stages of lymphocyte development. They also have important regulatory influences on other haematopoietic cells. Rapid progress is being made through the use of gene cloned cytokines in understanding the complex interactions of these factors with many different cell types. New factors have been added to the cytokine network, and new functions reported for existing cytokines. The clinical implications in disease and the application of cytokines or their inhibitors in human disorders, cancer, infection and autoimmunity, has met with some success and many trials are currently in progress which should lead to more successful therapeutic strategies.

Neuroimmune mechanisms of cytokine-induced depression: current theories and novel treatment strategies

The relationships between immune and neural function are an increasingly important area of study for neuropsychiatric disorders, in particular depression. This is exemplified by the growing number of publications on cytokines and depression during the last 10 years, as compared to earlier decades. This review summarizes the current theories and novel treatment strategies for depression, with a focus on cytokine-induced depression. Neuroimmune mechanisms are now viewed as central to the development of depressive symptoms and emerging evidence is beginning to identify the neural circuits involved in cytokine-induced depression. The current diagnostic categories for depression, as defined by the Diagnostic and Statistical Manual of Mental Disorders, however, are not etiologically or biologically derived, and it has been proposed that "depression", likely reflects multiple pathogeneses leading to varying symptom constellations. As we move toward a better biological understanding of depression-related symptom constellations or syndromes, the term "depression" may prove inadequately broad, and an integration of interdisciplinary literatures will increase in importance. Future research should aim to characterize these depression-related symptom constellations or syndromes better with the goal of optimizing treatment strategies.

Gamma interferon signaling in macrophage lineage cells regulates central nervous system inflammation and chemokine production

Intracranial (i.c.) infection of mice with lymphocytic choriomeningitis virus (LCMV) results in anorexic weight loss, mediated by T cells and gamma interferon (IFN-gamma). Here, we assessed the role of CD4(+) T cells and IFN-gamma on immune cell recruitment and proinflammatory cytokine/chemokine production in the central nervous system (CNS) after i.c. LCMV infection. We found that T-cell-depleted mice had decreased recruitment of hematopoietic cells to the CNS and diminished levels of IFN-gamma, CCL2 (MCP-1), CCL3 (MIP-1alpha), and CCL5 (RANTES) in the cerebrospinal fluid (CSF). Mice deficient in IFN-gamma had decreased CSF levels of CCL3, CCL5, and CXCL10 (IP-10), and decreased activation of both resident CNS and infiltrating antigen-presenting cells (APCs). The effects of IFN-gamma signaling on macrophage lineage cells was assessed using transgenic mice, called "macrophages insensitive to interferon gamma" (MIIG) mice, that express a dominant-negative IFN-gamma receptor under the control of the CD68 promoter. MIIG mice had decreased levels of CCL2, CCL3, CCL5, and CXCL10 compared to controls despite having normal numbers of LCMV-specific CD4(+) T cells in the CNS. MIIG mice also had decreased recruitment of infiltrating macrophages and decreased activation of both resident CNS and infiltrating APCs. Finally, MIIG mice were significantly protected from LCMV-induced anorexia and weight loss. Thus, these data suggest that CD4(+) T-cell production of IFN-gamma promotes signaling in macrophage lineage cells, which control (i) the production of proinflammatory cytokines and chemokines, (ii) the recruitment of macrophages to the CNS, (iii) the activation of resident CNS and infiltrating APC populations, and (iv) anorexic weight loss.

The reduction of voluntary physical activity after poly I:C injection is independent of the effect of poly I:C-induced interferon-beta in mice

One characteristic of sickness behavior in mice is demonstrated by a reduction in voluntary wheel-running activity during infection. Among synthetic double-stranded (ds) RNAs, polyriboinosinic: polyribocytidylic acid (poly I:C) activates to produce interferon (IFN) -beta, which plays an important role in anti-viral activity and host-defense. However, how voluntary wheel-running activity is regulated during poly I:C infection is unknown. To determine whether poly I:C-induced IFN-beta production is responsible for reduced spontaneous physical activity, we measured poly I:C-induced changes in voluntary wheel-running activity in mice. In this experiment, the mice were injected with poly I:C (0-5 mg/kg i.v.) and/or anti-IFN-beta neutralizing antibody (1.5x10(5) U/kg i.v.). We also observed the direct effect of injection of recombinant IFN-beta (rIFN-beta: 5.0x10(4) and 2.5x10(5) U/kg) on wheel-running behavior. Poly I:C treatment dose-dependently reduced wheel-running activity, and induced an increase in plasma IFN-beta in mice. However the activity was not attenuated by the neutralizing antibody specific to IFN-beta treatment. Additionally, the wheel-running activity in rIFN-beta treated mice was maintained, although they showed a higher IFN-gamma inducible protein (IP)-10 concentration in plasma compared with that of the vehicle group. Our results suggest that the transient reduction in physical activity after poly I:C injection is induced dose dependently, but that the mediator might not be poly I:C-induced IFN-beta.

Interferon: The pathways of discovery

This historical account covers 50 years of seminal research work on interferon done since its discovery in 1957. Topics related to molecular structure, production and action of interferons are considered from the viewpoint of how our insights have expanded and deepened within the context of evolving tools and general knowledge in cellular and molecular biology. Lines of thought that linked each discovery to the next are expounded.

Interferon and the central nervous system

Interferons (IFNs) were discovered as natural antiviral substances produced during viral infection and were initially characterized for their ability to "interfere" with viral replication, slow cell proliferation, and profound alteration of immunity. The IFNs are synthesized and secreted by monocytes, macrophages, T-lymphocytes, neurons, and glia cells. The different IFNs are classified into three classes: alpha, beta, and gamma. alpha-IFN produced in the brain exerts direct effects on the brain and endocrine system by activating the neurosecretory hypothalamic neurons and regulates the hypothalamic-pituitary-adrenocortical axis. IFNs modulate neurophysiological activities of many brain region involving in pain, temperature, and food intake regulation. alpha-IFN administration activates the sympathetic nerves innervating components of the immune system. IFNs may serve as regulatory mediators between the central nervous system, the immune system, and endocrine system. IFN is used as immunologic therapy to treat various hematologic malignancies and infectious ailments and autoimmune diseases.

Therapeutic Implications of Interferon Regulatory Factor (IRF)-1 and IRF-2 in Diffusely Infiltrating Astrocytomas (DIA): Response to Interferon (IFN)-β in Glioblastoma Cells and Prognostic Value for DIA

The precise mechanisms governing the direct effect of IFN-beta, including apoptosis induction, are not yet fully understood. To gain a better insight into these mechanisms, we investigated the signaling pathways focusing particularly on interferon regulatory factor 1 (IRF-1) and IRF-2 in glioblastoma cell lines. Furthermore, we attempted to determine whether or not IRF-1 and IRF-2 act as additional prognostic indicators in diffusely infiltrating astrocytomas (DIA). We first assessed the cytotoxic effects of IFN-beta based on a cell growth study and modified MTT assay, and then quantified the apoptosis using a sandwich enzyme immunoassay following IFN-beta treatment in the cell lines, U-87MG, T98G, and A-172. Subsequently, we carried out an analysis of apoptosis-related molecules as evaluated by densitometric analysis of Western blots, focusing on IRF-1 and IRF-2, and two major initiator caspases, caspase-8 and caspase-9. Furthermore, we assessed the expression of type I IFN receptor, IRF-1, and IRF-2 using immunohistochemical techniques in 63 DIA (15 of WHO grade II, 18 of grade III, and 30 of grade IV), and analyzed their impact on prognosis. An increase in apoptosis was apparent after 48 h of IFN-beta treatment (1 x 10(4) IU/ml) in T98G but not in U-87MG or A-172. IFN-beta treatment for 6 h significantly enhanced the expression of IRF-1 in all three cell lines. However, an enhanced expression of IRF-2 was observed only in the not-most-sensitive, non-apoptosis-induced U-87MG and A-172. While minimal processing of caspase-8 was noted in the three cell lines throughout the experiment, caspase-9 activation was observed in the apoptosis-detected T98G after 48 h of treatment, as indicated by a 1.33-fold increase (P=0.037). On the other hand, the IRF-1 LI and IRF-1/IRF-2 LI ratio were greater in low-grade DAI, and were negatively correlated with the histopathological grade in DIA (P=0.017 and P=0.001, respectively). Furthermore, the IRF-1/IRF-2 LI ratio was negatively correlated with the MIB-1 LI in DIA (P=0.004), and represented an independent and most powerful determinant of overall survival compared to other conventional prognostic factors (P=0.018). However, the relation was not statistically significant when only patients with high-grade DIA were assessed. Our findings suggest that up-regulation of IRF-1 and IRF-2 might be an important determinant of susceptibility to IFN-beta mediated cytotoxicity including apoptosis. Furthermore, the IRF-1/IRF-2 LI ratio may reflect the proliferative state of DIA and constitute an important prognostic marker in DIA. Thus, IRF-1 and IRF-2 could represent one of the therapeutic target sites for the regulation of cell growth in DIA.

Synthesis and biological properties of chimeric interferon-alpha2b peptides

We have previously reported the antiproliferative activity of synthetic sequences 29-35 and 122-139 of the interferon-alpha2b (IFN-alpha2b), both probably representing a common receptor recognition domain. In the search of new peptidic agonists, we designed and synthesized the linear peptide (Gly)2-122-137-Gly138-Gly29-30-35-(Gly)2, in which Gly residues replaced the 138 and 29 Cys bound through a disulfide bridge in the native cytokine. Additionally, a cyclic analog was obtained by reaction of the N- and C-terminal ends of the linear fragment. Thus, the distance that separates residues 122 and 35 in the crystalline structure of the IFN-alpha2b was maintained through a (Gly)4 bridge. When the influence of chimeric peptides on the proliferation of WISH cells was studied, it was shown that both derivatives significantly diminished cell growth. A more evident inhibitory effect on (125)I-IFN-alpha2b binding to WISH cell-membrane receptors was observed for both peptides. Results indicated that chimeric IFN-alpha2b peptides behaved as partial agonists of the IFN-alpha2b molecule and may be of interest for drug design purposes.

Biosynthesis of the IFN-γ binding protein of ectromelia virus, the causative agent of mousepox

Ectromelia virus (ECTV), the causative agent of mousepox, expresses an extracellular interferon-gamma binding protein (IFN-gammaBP) with homology to the ligand binding domains of the IFN-gamma high affinity receptor (IFN-gammaR1). Unlike the cellular receptor, the IFN-gammaBP binds IFN-gamma from several species. The IFN-gammaBP is synthesized early after infection, accumulating in the extracellular milieu as dimers composed of two protein species with Mr of 34.6 or 33.0 kDa. Homodimers are covalently linked by an interchain disulphide bond at position 216. The IFN-gammaBP has complex N-linked oligosaccharides at positions 41 and 149 as determined by site-directed mutagenesis and glycosidase treatment. Glycosylation at position 41 is required for secretion from mammalian cells and may play a role in the activity of the IFN-gammaBP. Glycosylation at position 149 is not required for secretion, and the lack of glycosylation at this site does not diminish ligand binding as measured by surface plasmon resonance (SPR) and ELISA.

Type I interferon receptor and response to interferon therapy in chronic hepatitis C patients: a prospective study

The type I interferon (IFN) receptor consists of at least two subunits, IFNAR1 and IFNAR2. We previously found a correlation between IFNAR1 and IFNAR2 expression in liver, and a correlation in IFNAR2 expression, but not in IFNAR1, between liver and peripheral blood mononuclear cells (PBMCs). The aim of this study was to prospectively assess whether IFNAR2 expression levels in PBMCs as well as in liver act as markers for predicting response to IFN therapy in chronic hepatitis C patients. Fifty-two Japanese patients with chronic hepatitis C, were enrolled. IFNAR2 mRNA was quantified using competitive polymerase chain reaction, in liver and PBMC specimens, and of the 52 patients assigned to receive a 6-month course of interferon-alpha therapy, 36 patients who received more than 300 million units of interferon were analysed. IFNAR2 mRNA expression levels were significantly higher in liver than in PBMCs in all 36 patients (P = 0.016). Seventeen sustained virologic responders showed lower pretreatment hepatitis C virus (HCV)-RNA levels (P = 0.017) in serum and higher pretreatment levels of IFNAR2 mRNA in liver (P = 0.007), but not in PBMCs, compared with nonsustained virologic responders. In multivariate analysis, these factors were independently associated with a sustained virologic response (i.e. HCV-RNA level: odds ratio 0.23, 95% CI 0.038-0.864; and IFNAR2 in liver: odds ratio 1.116, 95% CI 1.015-1.227). Hence, IFNAR2 expression levels in liver, but not in PBMCs, is predictive of response to IFN treatment in chronic hepatitis C patients.

Activation of protein kinase C delta by IFN-gamma

Engagement of the type II IFN (IFN-gamma) receptor results in activation of the Janus kinase-Stat pathway and induction of gene transcription via IFN-gamma-activated site (GAS) elements in the promoters of IFN-gamma-inducible genes. An important event in IFN-gamma-dependent gene transcription is phosphorylation of Stat1 on Ser(727), which is regulated by a kinase activated downstream of the phosphatidylinositol 3'-kinase. Here we provide evidence that a member of the protein kinase C (PKC) family of proteins is activated downstream of the phosphatidylinositol 3'-kinase and is engaged in IFN-gamma signaling. Our data demonstrate that PKCdelta is rapidly phosphorylated during engagement of the type II IFNR and its kinase domain is induced. Subsequently, the activated PKCdelta associates with a member of the Stat family of proteins, Stat1, which acts as a substrate for its kinase activity and undergoes phosphorylation on Ser(727). Inhibition of PKCdelta activity diminishes phosphorylation of Stat1 on Ser(727) and IFN-gamma-dependent transcriptional regulation via IFN-gamma-activated site elements, without affecting the phosphorylation of the protein on Tyr(701). Thus, PKCdelta is activated during engagement of the IFN-gamma receptor and plays an important role in IFN-gamma signaling by mediating serine phosphorylation of Stat1 and facilitating transcription of IFN-gamma-stimulated genes.

The p38 mitogen-activated protein kinase pathway and its role in interferon signaling

Interferons (IFNs) are pleiotropic cytokines that exhibit multiple biological effects on cells and tissues. IFN receptors are expressed widely in mammalian cells and virtually all different cell types express them on their surface. The Type I IFN receptor has a multichain structure, composed of at least two distinct receptor subunits, IFNalphaR1 and IFNalphaR2. Two Jak-kinases, Tyk-2 and Jak-1, associate with the different receptor subunits and are activated in response to IFNalpha or IFNbeta to regulate engagement of multiple downstream signaling cascades. These include the Stat-pathway, whose function is essential for transcriptional activation of IFN-sensitive genes, and the insulin receptor substrate pathway, which regulates downstream activation of the phosphatidyl-inositol-3' kinase. Members of the Map family of kinases are also activated by the Type I IFN receptor and participate in the generation of IFN signals. The p38 Map kinase pathway appears to play a very important role in the induction of IFN responses. p38 is rapidly activated during engagement of the Type I IFN receptor, and such an activation is regulated by the small G-protein Rac1, which functions as its upstream effector in a tyrosine kinase-dependent manner. The activated form of p38 regulates downstream activation of other serine kinases, notably MapKapK-2 and MapKapK-3, indicating the existence of Type I IFN-dependent signaling cascades activated downstream of p38. Extensive studies have shown that p38 plays a critical role in Type I IFN-dependent transcriptional regulation, without modifying activation of the Stat-pathway. It is now well established that the function of p38 is essential for gene transcription via ISRE or GAS elements, but has no effects on the phosphorylation of Stat-proteins, the formation of Stat-complexes, and their binding to the promoters of IFN-sensitive genes. As Type I IFNs regulate gene expression for proteins with antiviral properties, it is not surprising that pharmacological inhibition of the p38 pathway blocks induction of IFNalpha-antiviral responses. In addition, pharmacological inhibition of p38 abrogates the suppressive effects of Type I IFNs on normal human hematopoietic progenitors, indicating a critical role for this signaling cascade in the induction of the regulatory effects of Type I IFNs on hematopoiesis. p38 is also activated during IFNalpha-treatment of primary leukemia cells from patients with chronic myelogenous leukemia. Such activation is required for IFNalpha-dependent suppression of leukemic cell progenitor growth, indicating that this pathway plays a critical role in the induction of the antileukemic effects of IFNalpha.

Expression of the sodium channel transcripts Na(v)1.8 and Na(v)1.9 in injured dorsal root ganglion neurons of interferon-gamma or interferon-gamma receptor deficient mice

Changes in the dorsal root ganglion (DRG) expression of the sodium channels Na(v)1.8 and Na(v)1.9 may contribute to injury-induced hyperexcitability and pain. Interferon (IFN)-gamma receptor -/- mice display a reduced pain-related behavior after nerve injury as compared to wild-type mice (NeuroReport 8 (1997) 1311). To elucidate a possible role for IFN-gamma in the regulation of sodium channels, we have studied the DRG mRNA expression of Na(v)1.8/Na(v)1.9 in IFN-gamma- or IFN-gamma receptor-deficient mice. In both types of mice, nerve damage induced a downregulation of Na(v)1.8 as well as Na(v)1.9. The magnitude of this reduction was similar to that observed in wild-type animals. These results indicate that the downregulation of Na(v)1.8/Na(v)1.9 in damaged DRG neurons is not influenced by IFN-gamma. Thus, the reduced pain-related behavior of nerve-injured IFN-gamma receptor null mice is not due to differential changes in the regulation of Na(v)1.8/Na(v)1.9 mRNA.

Seeing the light: preassembly and ligand-induced changes of the interferon gamma receptor complex in cells

Our experiments were designed to test the hypothesis that the cell surface interferon gamma receptor chains are preassembled rather than associated by ligand and to assess the molecular changes on ligand binding. To accomplish this, we used fluorescence resonance energy transfer, a powerful spectroscopic technique that has been used to determine molecular interactions and distances between the donor and acceptor. However, current commercial instruments do not provide sufficient sensitivity or the full spectra to provide decisive results of interactions between proteins labeled with blue and green fluorescent proteins in living cells. In our experiments, we used the blue fluorescent protein and green fluorescent protein pair, attached a monochrometer and charge-coupled device camera to a modified confocal microscope, reduced background fluorescence with the use of two-photon excitation, and focused on regions of single cells to provide clear spectra of fluorescence resonance energy transfer. In contrast to the prevailing view, the results demonstrate that the receptor chains are preassociated and that the intracellular domains move apart on binding the ligand interferon gamma. Application of this technology should lead to new rapid methods for high throughput screening and delineation of the interactome of cells.

Functional analysis of mouse hepatocytes differing in DNA content: volume, receptor expression, and effect of IFNgamma

Polyploidy and binuclearity are characteristics of the mammalian liver. Increasing polyploidisation occurs with age and after administration of various drugs and chemicals. This study was designed to examine the function of ploidy by addressing several questions: (1) Does the increase in size of polyploid hepatocytes have any physiological function by altering surface receptor expression such as intercellular adhesion molecule-1 (ICAM-1, CD54) or IFNgammaR? and (2) Do polyploid cells respond differently to inflammatory cytokines such as interferon gamma (IFNgamma)? We have developed a method to accurately measure the volume of live isolated hepatocytes using confocal microscopy and image analysis. Using flow cytometry, we have shown that the expression of ICAM-1 increases with increasing DNA content and IFNgammaR is not detectable on isolated mouse hepatocytes. Diploid (2n), tetraploid (4n) and octoploid (8n) hepatocytes were found to be equally susceptible to IFNgamma-induced apoptosis in vitro. Although the function of polyploidy remains unanswered, we have described some of the characteristics of polyploidy in isolated hepatocytes and in vitro.

Amino acid substitutions in loop BC and helix C affect antigenic properties of helix D in hybrid IFN-alpha21a/alpha2c molecules

We compared the antigenic properties of human interferon-alpha2c (IFN-alpha2c), IFN-alpha21a, hybrids IFN-alpha21a/alpha2c, and their mutants, using a panel of 27 anti-IFN-alpha1, anti-IFN-alpha2, and anti-IFN-alpha8/1/8 monoclonal antibodies (mAb). After immunoanalysis by ELISA, we found parental IFN-alpha2c and IFN-alpha21a to be antigenically distinct. Lack of reactivity of anti-IFN-alpha1 mAb with IFN-alpha21a indicated an antigenic distinction between subtypes alpha1 and alpha21a. The antigenic properties of hybrid IFNs consisting of the N-terminal portion (1-75) of IFN-alpha21a and the C-terminal portion (76-166) of IFN-alpha2c were analyzed with mAb recognizing defined regions of IFN-alpha2c, IFN-alpha1, and IFN-alpha8/1/8. We found that extending the sequence of IFN-alpha21a up to position 95 in hybrid molecule decreased the immunoreactivity of mAb specific for the antigenic structure formed by residues --112-132-- (helix D) of IFN-alpha2c. Inserting the sequence 76-81 (loop BC) of IFN-alpha2c into the sequence of 1-95 of IFN-alpha21a restored the reactivity of anti-IFN-alpha2c mAb. Some amino acid substitutions at positions 86 and 90 (helix C) of hybrid IFN-alpha21a/alpha2c also affected the immunoreactivity of C-terminal-specific mAb, which recognize helix D, but did not influence the structure of C-terminus of IFN (aa 151-165). Changes in the structure of constructs affected not only their antiproliferative activity but also their antiviral activity on human cells.

Biologic responses to IFN-alpha administration in humans

Although interferon-alpha (IFN-alpha) was discovered over 40 years ago, it was many years before it was registered as a therapeutic agent. Because of its unique qualities, it has been registered for both antiviral and antitumor indications. In addition to its therapeutic effects in viral diseases and cancer, IFN-alpha interferes with several important physiologic systems. It interacts with the immune system and affects several neuroendocrine and metabolic circuits. The specific mechanisms by which IFN-alpha exerts its therapeutic effects are complex, and it is very difficult to tie the biologic actions of IFN-alpha to specific clinical effects.

Suitable experimental conditions are required to characterize interferon-alpha2b synthetic peptides

The binding and antiproliferative activities of synthetic peptides 29-35 and 122-139 of interferon-alpha2b, both of which contain a cysteine residue in their sequences, were studied in the presence or absence of a dissociation medium containing mainly urea, dithiothreitol and 2-mercaptoethanol. Although interferon-alpha2b peptides either did not modify or slightly increased 125I-labelled interferon-alpha2b specific binding to WISH cell-membrane receptors in the absence of dissociation medium, significant binding inhibition was obtained when both peptides were assayed in dissociation medium. Furthermore, also in the presence of dissociating agents, the two fragments inhibited cell growth in a concentration-dependent manner, the 122-139 sequence being more effective than the 29-35 sequence. No additive effect on interferon binding and cell proliferation was observed when both peptides were added simultaneously. Results obtained after submitting peptide 122-139 to gel filtration or PAGE under different experimental conditions showed the presence of dimers and/or noncovalent aggregates arising from intermolecular disulfide bridges or hydrophobic interactions. Thus, our results indicated that peptide effects on 125I-labelled interferon-alpha2b binding and WISH cell proliferation were clearly manifested when the amount of monomeric species increased, showing that suitable experimental conditions should be used to study peptide behavior. The ability of both peptides to effectively trigger an interferon-specific biological action, such as cell growth inhibition, strongly suggested that 29-35 and 122-139 interferon-alpha2b fragments constitute the conformational epitope or mimotope that interacts with the cytokine-specific receptor.

The production and biological assessment of cervine interferon gamma

Cervine interferon gamma (IFN-gamma) was cloned and expressed using an Escherichia coli expression system pET-32. The expressed protein contained a 6 histidine purification tag and an 11 kDa thioredoxin fusion partner 5' to the IFN-gamma molecule. The ability of IFN-gamma to inhibit the killing of Madin-Darby bovine kidney cells by Semliki forest virus was used as a measure of the bioactivity of the recombinant cervine IFN-gamma (rIFN-gamma). It was shown that the presence of the thioredoxin fusion partner 5' to the IFN-gamma molecule did not affect its biological activity. As in the mouse model, it was shown that cervine rIFN-gamma was able to down-regulate the transcription of interleukin 10 mRNA while up-regulating the transcription of interleukin 12 mRNA in lipopolysaccharide-sensitized, peripheral blood mononuclear cells. A prototype ELISA was tested for its ability to detect both recombinant and native IFN-gamma. The ELISA was able to detect rIFN-gamma at concentrations greater than 100 pg/ml. It was also used to detect native IFN-gamma produced by peripheral blood lymphocytes from Mycobacterium bovis infected or vaccinated deer after in vitro restimulation with antigen. The rIFN-gamma and the cervine IFN-gamma specific ELISA provide valuable tools with which to study important zoonotic infections in farmed and wild deer.

Peripheral nerve injury induces endoneurial expression of IFN-gamma, IL-10 and TNF-alpha mRNA

Axotomy of a peripheral nerve leads to interruption of axon continuity with Wallerian degeneration in the distal segment and regenerative events in the proximal remaining neuron. Local inflammation is a consequence of trauma in general and signal molecules regulating inflammation, such as cytokines, participate in the outcome of nerve trauma. We studied a broad set of potent immunoregulatory cytokines after transection of rat sciatic nerve. The endoneurium of the transected rat sciatic nerve was taken from both proximal and distal stumps. The pooled endoneurium of 6 rats was studied using reverse transcription polymerase chain reaction (RT-PCR) after 14 h; 1, 3, 5, 7 days; 2 and 4 weeks after transection. A new observation was that TNF-alpha mRNA showed phasic expression pattern; three distinct peaks were seen, immediately (14 h), after 5 days and in the distal part also after 2 weeks. This phenomenon may be related to the breakdown of the blood-nerve barrier and to the recruitment of circulating macrophages. We further noticed that IFN-gamma mRNA was expressed between 5 days and 2 weeks. This suggests that T-cells may also take part in the regenerative processes. Furthermore, we observed that IL-10 mRNA is expressed continuously during Wallerian degeneration. The continuous expression of IL-10 mRNA may attenuate the production of inflammatory cytokines by macrophages and other cells.

The human interferon alpha species and receptors

Interferon (IFN) was approved by the U.S. Food and Drug Administration on June 5, 1986. As the first biotherapeutic approved, IFN-alpha paved the way for development of many other cytokines and growth factors. Nevertheless, we have just touched the surface of understanding the multitude of human IFNs. This paper reviews the history of the purification of human leukocyte IFN and key aspects of our current state of knowledge of human interferon alpha genes, proteins, and receptors.

Identification of a linear epitope of interferon-alpha2b recognized by neutralizing monoclonal antibodies

Four monoclonal antibodies (mAbs) directed against the recombinant human interferon-alpha2b (IFN-alpha2b) were used as probes to study the interaction of the IFN molecule to its receptors. The [125I]IFN-alpha2b binding to immobilized mAbs was completely inhibited by IFN-alpha2b and IFN-alpha2a but neither IFNbeta nor IFNgamma showed any effect. Gel-filtration HPLC of the immune complexes formed by incubating [125I]IFN-alpha2b with paired mAbs revealed the lack of simultaneous binding of two different antibodies to the tracer, suggesting that all mAbs recognize the same IFN antigenic domain. Furthermore, the mAbs were also able to neutralize the IFN-alpha2b anti-viral and anti-proliferative activities as well as [125I]IFN-alpha2b binding to WISH cell-membranes. As [125I]mAbs did not recognize IFN exposed epitopes in the IFN:receptor complexes, mAb induction of a conformational change in the IFN binding domain impairing its binding to receptors was considered unlikely. In order to identify the IFN region recognized by mAbs, IFN-alpha2b was digested with different proteolytic enzymes. Immunoreactivity of the resulting peptides was examined by Western blot and their sequences were established by Edman degradation after blotting to poly(vinylidene difluoride) membranes. Data obtained indicated that the smallest immunoreactive region recognized by mAbs consisted of residues 107-132 or 107-146. As this zone includes the sequence 123-140, which has been involved in the binding to receptors, and our mAbs did not show an allosteric behaviour, it is concluded that they are directed to overlapping epitopes located close to or even included in the IFN binding domain.

Preliminary results of the alternating administration of natural interferon-alpha and recombinant interferon-gamma for metastatic renal cell carcinoma

OBJECTIVE

To evaluate the efficacy and toxicity of the alternating administration of natural (n) interferon (IFN)-alpha and recombinant (r) IFN-gamma for metastatic RCC.

PATIENTS AND METHODS

The study comprised 24 patients (median age 60 years, range 42-77), 20 of whom were evaluable for response and all 24 evaluable for toxicity. Initially, nIFN-alpha was administered subcutaneously on days 1 and 3, and rIFN-gamma on day 2, for 1-2 weeks in the evening or at night, both at doses of 3 MU. If this regimen was tolerated, nIFN-alpha and rIFN-gamma were administered at the same doses on days 1, 3 and 5, and on days 2 and 4, respectively.

RESULTS

There were three complete remissions and two partial remissions, giving a total response rate of 25%. All responders (complete plus partial remission) had undergone nephrectomy. Multiple lung metastases completely disappeared from four responders. The median and maximum time to remission in the responders were 2 and 7 months, respectively. The survival time of the responders was significantly longer than that of those not responding (stable and progressive disease, P=0.0202). Toxicities were mostly limited to WHO grades 1 and 2, with grade 3 leucopenia and grade 4 hepatic dysfunction in only one patient each. These toxicities were transient and there were no treatment-related deaths.

CONCLUSION

The alternating administration of nIFN-alpha and rIFN-gamma is an effective treatment for metastatic RCC. This treatment is particularly suitable for patients who have undergone nephrectomy and have lung metastases.

Enhancement of immobility in mouse forced swimming test by treatment with human interferon

We investigated the depression induced by human interferons using the forced swimming test in mice. Intravenous (i.v.) administration of interferon-alpha s (natural interferon-alpha, recombinant interferon-alpha-2a and recombinant interferon-alpha-2b, 600-60000 IU/kg) increased the immobility time in the forced swimming test in a dose-dependent manner, but natural interferon-beta and recombinant interferon-gamma-1a did not affect the immobility time. The increase in the immobility time induced by recombinant interferon-alpha-2b peaked at 15 min after dosing. Administration of recombinant interferon-alpha-2b (6000 IU/kg, i.v.) once daily for 7 consecutive days increased the immobility time, but natural interferon-beta and recombinant interferon-gamma-la did not. Recombinant interferon-alpha-2b in combination with the anti-depressants imipramine (10 mg/kg, i.p.) and mianserin (20 mg/kg, i.p.) did not increase the immobility time. These results suggest that interferon-alpha has a greater potential for inducing depression than interferon-beta and -gamma, and that anti-depressants are effective against interferon-alpha-induced depression.

Interferons in dermatology. Present-day standard

Since the first clinical trials in the early 1980s with recombinant interferon, it was possible to show for a variety of indications that cytokines, especially interferons, at certain doses and at respective intervals, when applied in combination with other pharmaceutical compounds open new powerful therapeutic possibilities. Worldwide, recombinant interferon is licensed, especially in dermato-oncology, for the indication of HIV-associated Kaposi's sarcoma, cutaneous T-cell lymphoma, and recently for adjuvant therapy of high-risk malignant melanoma. Recombinant interferon is at present not licensed for dermatologic indication (septic granulomatosis). At the end of our century the indication spectrum for interferons as monotherapy and as combination therapy will undoubtedly be extended. Larger and controlled studies will prove the importance of interferons in dermato-oncology as well as in inflammatory and infectious dermatoses. The combination of interferons with standard therapies will surely be of the utmost importance in dermatotherapy.

Crystallization and preliminary X-ray analysis of a 1:1 complex between a designed monomeric interferon-gamma and its soluble receptor

A variant of human interferon-gamma (IFN-gamma) has been created in which the two chains of the homodimeric cytokine were linked N- to C-terminus by an eight residue polypeptide linker. The sequence of this linker was derived from a loop in bira bifunctional protein, and was determined from a structural database search. This "single-chain" variant was used to create an IFN-gamma molecule that binds only a single copy of the alpha-chain receptor, rather than the 2 alpha-chain receptor: 1 IFN-gamma binding stoichiometry observed for the native hormone. Crystals have been grown of a 1:1 complex between this single-chain molecule and the extracellular domain of its alpha-chain receptor. These crystals diffract beyond 2.0 A, significantly better than the 2.9 A observed for the native 2:1 complex. Density calculations suggest these crystals contain two complexes in the asymmetric unit; a self-rotation function confirms this conclusion.

Structure-Function Study of the Extracellular Domain of the Human IFN-α Receptor (hIFNAR1) Using Blocking Monoclonal Antibodies: The Role of Domains 1 and 2

We have performed a structure-function analysis of extracellular domain regions of the human IFN-α receptor (hIFNAR1) using mAbs generated by immunizing mice with a soluble hIFNAR1-IgG. Five mAbs described in this study recognize different epitopes as determined by a competitive binding ELISA and by alanine substitution mutant analyses of the hIFNAR1-IgG. Two mAbs, 2E1 and 4A7, are able to block IFN-stimulated gene factor 3 (ISGF3) formation and inhibit the antiviral cytopathic effect induced by several IFN-α (IFN-α2/1, -α1, -α2, -α5, and -α8). None of these anti-IFNAR1 mAbs were able to block activity of IFN-β. mAb 4A7 binds to a domain 1-hIFNAR1-IgG but not to a domain 2-hIFNAR1-IgG, which suggests that its binding region is located in domain 1. The binding of the most potent blocking mAb, 2E1, requires the presence of domain 1 and domain 2. The most critical residue for 2E1 binding is a lysine residue at position 249, which is in domain 2. These findings suggest that both domain 1 and domain 2 are necessary to form a functional receptor and that a region in domain 2 is important. IFN-β recognizes regions of the hIFNAR complex that are distinct from those important for the IFN-α.

Differential use of the betaL subunit of the type I interferon (IFN) receptor determines signaling specificity for IFNalpha2 and IFNbeta

The signaling specificity for cytokines that have common receptor subunits is achieved by the presence of additional cytokine-specific receptor components. In the type I interferon (IFN) family, all 14 subtypes of IFNalpha, IFNbeta, and IFNomega bind to the same alpha and betaL subunits of the type I IFN-R, yet differences in signaling and biological effects exist among them. Our data demonstrate that IFNalpha2 and IFNbeta utilize different regions of the betaL subunit for signaling. Thus, in contrast to other cytokine systems, signal diversity in the type I IFN system can be accomplished within the same receptor complex by utilizing different regions of the same receptor subunits.

Interferons Alpha, Beta, and Omega

Interferon alpha (IFN-α) is a mixture of closely related proteins, termed “subtypes,” expressed from distinct chromosomal genes. Interferon β (IFN-β) is a single protein species and is molecularly related to IFN-α subtypes, although it is antigenically distinct from them. IFN omega (IFN-ω) is antigenically distinct from IFN-α and IFN-β but is molecularly related to both. The genes of three IFN subtypes are tandemly arranged on the short arm of chromosome 9. They are transiently expressed following induction by various exogenous stimuli, including viruses. They are synthesized from their respective mRNAs for relatively short periods following gene activation and are secreted to act, via specific cell surface receptors, on other cells. IFN-α subtypes are secreted proteins and as such are transcribed from mRNAs as precursor proteins, pre-IFN-α, containing N-terminal signal polypeptides of 23 hydrophobic amino acids (aa) mainly. Pre-IFN-β contains 187 aa, of which 21 comprise the N-terminal signal polypeptide and 166 comprise the mature IFN-β protein. IFN-ω contains 195 aa—the N-terminal 23 comprising the signal sequence and the remaining 172, the mature IFN-ω protein. At the C-terminus, the aa sequence of IFN-ω is six residues longer than that of IFN-α or IFN-β proteins. IFN-α, as a mixture of subtypes, and IFN-ω may be produced together following viral infection of null lymphocytes or monocytes/macrophages. The biological activities of IFNs are mostly dependent upon protein synthesis with selective subsets of proteins mediating individual activities. IFNs can also stimulate indirect antiviral and antitumor mechanisms, depending upon cellular differentiation and the induction of cytotoxic activity.

The interferon gamma (IFN-gamma) receptor: a paradigm for the multichain cytokine receptor

With the purification and cloning of the interferon gamma (IFN-gamma) receptor chains the mechanism of IFN-gamma action and the resultant signal transduction events were delineated in remarkable detail. The interferon gamma (IFN-gamma) receptor complex consists of two chains: IFN-gammaR1, the ligand-binding chain, and IFN-gammaR2, the accessory chain. Binding of IFN-gamma causes oligomerization of the two IFN-gamma receptor subunits, IFN-gammaR1 and IFN-gammaR2, which initiates the signal transduction events: activation of Jak1 and Jak2 receptor associated protein tyrosine kinases, phosphorylation of the IFN-gammaR1 intracellular domain on Tyr440 followed by phosphorylation and activation of Stat1alpha, the latent transcriptional factor. With all these steps established, the IFN-gamma receptor complex has provided the basic model for understanding the receptors for other members of the family of class II cytokine receptors.

A type I interferon signaling factor, ISF21, encoded on chromosome 21 is distinct from receptor components and their down-regulation and Is necessary for transcriptional activation of interferon-regulated genes

The type I interferons (IFNs) are a family of cytokines, comprising at least 17 subtypes, which exert pleiotropic actions by interaction with a multi-component cell surface receptor and at least one well characterized signal transduction pathway involving JAK/STAT (Janus kinase/signal transducer and activator of transcription) proteins. In a previous report, we showed that a signaling factor, encoded by a gene located on the distal portion of chromosome 21, distinct from the IFNAR-1 receptor, was necessary for 2'-5'-oligoadenylate synthetase activity and antiviral responses, but not for high affinity ligand binding. In the present studies using hybrid Chinese hamster ovary cell lines containing portions of human chromosome 21, we show that the type I IFN signaling molecule, designated herein as ISF21, is distinct from the second receptor component, IFNAR-2, which is expressed in signaling and non-signaling cell lines. The location of the gene encoding ISF21 is narrowed to a region between the 10;21 and the r21 breakpoints, importantly eliminating the Mx gene located at 21q22.3 (the product of which is involved in IFN-induced antiviral responses) as a candidate for the signaling factor. To characterize the action of this factor in the type I IFN signaling pathway, we show that it acts independently of receptor down-regulation following ligand binding, both of which occur equally in the presence or absence of the factor. In addition, we demonstrate that ISF21 is necessary for transcriptional activation of 2'-5'-oligoadenylate synthetase, 6-16, and guanylate-binding protein gene promoter reporter constructs, which are mediated by several signaling pathways. ISF21 represents a novel factor as the localization to chromosome 21, and the data presented in this study exclude any of the known type I IFN signal-transducing molecules.

HIV-1 p17 and IFN-gamma both induce fructose 1,6-bisphosphatase

The p17 matrix protein of the human immunodeficiency virus type 1 (HIV-1) plays a crucial role in AIDS pathogenesis. It orchestrates viral assembly and directs the preintegration complex to the nucleus of infected cells. Recently, the three-dimensional structure of p17 was shown to resemble that of interferon-gamma (IFN-gamma), suggesting that both proteins might share analogous functions. We demonstrate that in monocytes, p17 shares with IFN-gamma the ability to induce 1alpha-hydroxylase activity and to activate fructose 1,6-bisphosphatase gene expression in the presence of 25-hydroxyvitamin D3. However, p17 does not bind to the IFN-gamma cell membrane receptor and fails to increase expression of IFN-gamma-induced proteins, such as tryptophanyl-tRNA synthetase, Fc gammaRI, and HLA DR or B7/BB1 antigens. Altogether, our results raise the possibility that the structural resemblance between p17 and IFN-gamma causes the selective activation of a common pathway resulting in the production of 1,25-dihydroxyvitamin D3. We also found that unlike IFN-gamma, p17 increases the intracellular ATP content. Since transport of the HIV-1 preintegration complex through the nuclear membrane is an ATP-dependent process, our observation suggests that p17 plays a double role in this active transport, not only by acting as a chaperone molecule but also by recruiting the necessary energy for this process.

Anti-tumor activity of synthetic peptide fragments of the human interferon-alpha 2

We have studied an influence of nine overlapping peptides from the region between amino acid residues 124 and 144 of the human interferon (FIN)-alpha 2 molecule on the growth of human lymphoid tumor cell lines in vitro. It was found that several, but not all, synthetic peptides inhibited proliferation of the same cell lines that IFN did. One of peptides, corresponding to the 124-138 amino acid residues of the IFN molecule (124-138) was most active. Using a human-mouse somatic hybrid cell line, we have shown that antiproliferative activity of the peptide 124-138 and IFN depended on the presence of human chromosome 21. Receptor binding studies also demonstrated that the peptide specifically interacted with membrane receptors on hybrid human-mouse cells carrying human chromosome 21, but not on parental mouse cells. Displacement experiments confirm that IFN and the peptide 124-138 compete for the same binding sites. Taken together, the data presented support a hypothesis that the C-terminal part of the IFN molecule contributes to antiproliferative activity possessed by IFN. Synthetic peptides studied in the present work may serve as a tool for studying tumor cell growth regulation by IFN and may be considered as potential nontoxic anti-tumor agents.

Isolation of a biologically active soluble human interferon-alpha receptor-GST fusion protein expressed in Escherichia coli

The cDNA encoding the extracellular domain of the human interferon-alpha (IFN-alpha) receptor (Uzé, G., Lutfalla, G., and Gresser, I. Cell 1990;60:225-234) lacking the signal peptide has been expressed in Escherichia coli as a fusion protein with glutathione S-transferase. The fusion protein represented 12% of total bacterial proteins and was found exclusively within cytoplasmic inclusion bodies. Inclusion body material was completely solubilized by 8 M urea; 20% solubilization was achieved by cell lysis in the presence of 0.45% cholamidopropyl dimethylammoniol-propane sulfonate and 1% Triton X-100. The soluble fusion protein was purified by gel filtration and affinity chromatography. Overall recovery of affinity purified fusion protein was approximately 100-200 micrograms/liter of cell culture. The affinity purified and refolded fusion protein exhibited the expected amino terminal sequence and M(r) of 68,000 on reduced sodium dodecylsulfate gel electrophoresis. The protein reacted with antibodies specific for the cloned IFN-alpha receptor and inhibited the antiviral and antiproliferative activities of recombinant IFN-alpha B. We have demonstrated that the fusion protein binds to IFN-alpha B and competes with the cell surface receptor for binding to this IFN-alpha species.

Purification and crystallization of a complex between human interferon gamma receptor (extracellular domain) and human interferon gamma

X-ray diffraction quality crystals have been obtained from a complex between interferon gamma and the extracellular domain of its high-affinity cell surface receptor. The crystals were obtained from interferon gamma/interferon gamma receptor complexes purified by size exclusion chromatography. Diffraction quality crystals required analyzing these complex samples by isoelectric focusing gels to select purified complex fractions devoid of unbound interferon gamma. These studies used interferon gamma receptor engineered with an eight amino acid N-terminal deletion to eliminate heterogeneity generated due to proteolytic cleavage. In addition, the receptor was expressed in an E. coli secretion cell line which eliminated the need to refold the protein. Hexagonal crystals were grown from 1.6 M ammonium phosphate solutions and belong to a spacegroup of P6(5)22 with unit cell dimensions a = 145.9 A and c = 180.3 A. These crystals diffract to at least 2.9 A resolution when exposed to synchrotron radiation. SDS PAGE analysis of the crystals demonstrated that both interferon gamma and the receptor were present. Analysis of the x-ray diffraction data revealed that the crystals contain complexes with a stoichiometry of 2:1 receptor: ligand within the crystallographic asymmetric unit and consist of approximately 55% solvent.

Binding of interferon-alpha and -beta to a component of the human type I interferon receptor expressed in simian cells

The type I interferons (IFNs) are a family of homologous cytokines that compete for receptor binding. Past experiments with a cloned human IFN-alpha receptor component (designated herein as HuIFNAR-1) transfected into different cell backgrounds have given contradictory results in terms of binding and signalling after exposure of cells to different human type I IFNs. In order to investigate the binding specificity of human type I IFN subtypes to HuIFNAR-1, a cDNA encoding HuIFNAR-1 was transfected into simian COS cells. HuIFNAR-1 expression in COS cells, which was confirmed by Northern blot analysis, resulted in increased binding of 125I-labelled HuIFN-alpha 2 and -beta. These data support the participation of this receptor component in ligand binding, probably in association with other receptor components.

The effect of interferon-alpha on the pituitary-adrenal axis

This report concerns the use of a minimum stress animal model for evaluating the neuromodulatory effects of interferon-alpha (IFN-alpha). Male Sprague-Dawley rats, 350-450 g, received jugular catheters and were habituated to handling and sampling arenas. These procedures will minimize stress usually associated with i.v. injections and blood sampling. Natural rat IFN-alpha/beta (RaIFN-alpha/beta) endotoxin free (Lee Biomolecular Research Laboratories, San Diego, CA) or recombinant human IFN-alpha, (rHuIFN-alpha) (a gift from Hoffman La Roche, Nutley, NJ) was injected into rats via catheter at various IFN concentrations. Controls were injected with either (1) vehicle (saline), (2) human or bovine serum albumin in saline, or (3) heat-denatured RaIFN-alpha/beta. Experiments were begun (0 h) at about 0900 h, and blood samples were withdrawn at intervals up to 2 h after IFN or control injections and replaced by the same volume of saline. The concentrations of corticosterone and ACTH in peripheral plasma were measured by radioimmunoassay. Both IFN, when injected at concentrations of 300 or 600 U/g body weight (U/gbw), stimulated an increase above 0 h levels of both hormones in the same animals. Additionally, the stimulation was also evident when compared with plasma hormone levels in animals injected with control substance in a parallel time course. After administration of 150 U/gbw of either IFN, only the increase in the blood corticosterone was significant. These studies demonstrate that both homospecific (RaIFN-alpha/beta) and heterospecific (rHuIFN-alpha) IFN preparations are capable of stimulating the pituitary-adrenal axis.