The hormonal concept of interferon. Brief review

The role of IFN-alpha as homeostatic agent in the inflammatory response: a balance between danger and response?

Interferon-alpha (IFN-alpha) is thought of by most immunologists as a fundamental component of the antiviral innate immune response, with other, accessory properties. Several lines of evidence point to a fundamental reappraisal of this conceptual framework because it may neglect other crucial functions of this cytokine under both health and disease conditions. Among these, a regulatory role in the inflammatory response is probably of paramount importance, as shown by in vivo and in vitro studies on humans, pets, and farm and laboratory animals. This role would not conflict with the main functions of IFN-alpha in the innate immune system and would complement these in line with major, evolution-based needs of the host. A hinge role of IFN-alpha between innate and adaptive immunity was recognized in the past on the basis of compelling evidence. This concept should now be widened; not only does IFN-alpha act to trigger, amplify, and sustain the different phases of the immune response, but it could also promote a substantial balance between danger and inflammatory response when an infectious challenge is either declining or completely over.

The role of IL-4 in human myeloid leukemia: stimulation of RNA synthesis and transduction of differentiation signals through an IL-4 receptor leads to functional and HLA positive HL-60 cells

The ectopic expression of lineage markers on irrelevant cell types may be of importance in the differentiation pathway(s) of these cells. One example, that is the subject of this study, is the presence of the interleukin-4 (IL-4) receptor on the surface of the human HL-60 myeloid leukemia cell line. The presence of such a receptor, that at first seems to be a simple genetic misprogramming, has an unusual biological function: It serves as a bridge to link the B cell growth factor IL-4 in order to transduce a number of differentiation signals in this M2 acute myeloid leukemia (AML) population. Signal transduction is followed by stimulation of RNA synthesis and subsequent induction of differentiation. Daily administration of low IL-4 dose yields proliferative senescent cells that exhibit 66% of growth inhibition in a 5-day tritiated thymidine incorporation assay. These cells clearly exit from the standard M2 morphology and show more mature characteristics as assessed by the Giemsa-Wright staining technique, followed by a 2-fold increase of the monocyte-granulocyte-specific Mac-1 surface antigen. Cellular function is also affected positively since phagocytosis of latex beads increases considerably after IL-4 treatment. Finally, as reported for normal human and murine monocytes and macrophages, the receptor-ligand interaction augments the levels of the class I and class II antigenic determinants by approximately 60%. Our results suggest that ectopic expression of markers may be a "distinct" event required during a short period in the differentiation of certain hemopoietic cells leading to mature and normal phenotypes.

Different molecular mechanisms lead to same endpoints with different function: TNF-alpha induces non-functional CSF-1 receptors on HL-60 cells in contrast to interferon-gamma

Tumour necrosis factor-alpha (TNF-alpha) induces differentiation on human promyelocytic leukemia cells (HL-60) as assessed by growth inhibition accompanied by reduction of c-myc levels, and expression of surface colony-stimulating factor-1 (CSF-1) receptors reported as molecular markers for acute myeloid leukemia (AML). CSF-1 receptors can be readily demonstrated by direct binding of 125I-CSF-1 and expression of v-fms whose gene product retains a complete ligand binding domain. Although the same findings have been previously demonstrated on HL-60 cells after interferon-gamma (IFN-gamma) treatment, the major difference between the two pathways of cellular differentiation is the functional state of the induced receptors: when IFN-gamma is used as differentiation agent, the cells are driven to express a high number of CSF-1 receptors and are able to respond to a CSF-1 stimulus. Such mitogenic response is not obtained when TNF-alpha is applied as inducer indicating that the newly expressed receptors are not functional. This difference may be due to different molecular mechanisms the two factors trigger in order to reach the same endpoint: the maturation of this leukemic population.

Recombinant interferon-gamma applied to the brain ventricular system protects rats against pseudorabies

We examined the prophylactic efficacy of recombinant rat interferon-gamma (IFN-gamma) administered directly into the brain ventricular system or via the intraperitoneal (i.p.) route against central and peripheral pseudorabies virus (PRV) infection. Intraperitoneally given IFN-gamma completely protected rats against a lethal i.p. PRV infection. The same regimen showed no protective effect against lethal intracerebroventricular (i.c.v.) PRV challenge even if IFN-gamma was given in high concentrations. When given via the i.c.v. route, IFN-gamma protected rats against lethal i.c.v. infection and also evoked partial protection with extended survival times of i.p. infected rats. Our results demonstrate an IFN-gamma-mediated antiviral effect in the central nervous system.

Alpha interferon therapy for haematological malignancies: correlation between in vivo induction of the 2',5'oligoadenylate system and clinical response

2',5'oligoadenylate (2-5A) synthetase mRNA and enzyme levels have been studied in peripheral blood mononuclear cells from 12 patients with chronic granulocytic leukaemia (CGL), 14 with essential thrombocythaemia (ET) and nine with chronic lymphocytic leukaemia (CLL), undergoing therapy with alpha interferon (alpha IFN). 2-5A synthetase mRNA was assayed by hybridization using the dot-blot technique and the enzyme activity was measured biochemically. A statistically significant difference was observed (P less than 0.05) between the degree of in vivo induction of mRNA by IFN alpha in the total patients between the good and intermediate responders and the poor responders. There was a similar pattern in each of the CGL, ET and CLL groups although this only reached statistical significance in the CGL group. In vitro induction of either mRNA or of enzyme activity, however, did not show a difference between the responders and poor responders in any of the patient groups. Our findings are consistent with the concept that 2-5A has an important role in the anti-tumour activity of alpha IFN and suggest that measurement of in vivo induction of 2-5A synthetase mRNA may be useful in predicting clinical response. In vitro studies, on the other hand, do not provide a reliable predictor of clinical response.

Gastrointestinal carcinoid tumours. Histogenetic, histochemical, immunohistochemical, clinical and therapeutic aspects

The increased knowledge of the pathobiology of gastrointestinal carcinoid (neuroendocrine) tumours and the improved therapeutic possibilities have brought a demand for more precise diagnosis. Although the carcinoid tumours can often be tentatively recognized in routinely processed microscopic slides, their more accurate identification requires additional diagnostic procedures. General neuroendocrine markers such as the argyrophil reaction of Grimelius and immunohistochemistry with application of antibodies against chromogranin A and of neuron-specific enolase are discriminatory staining methods which are used to reveal the neuroendocrine origin of almost all highly differentiated carcinoid tumours of the gastrointestinal tract. Mid-gut carcinoids, which predominate among these tumours almost unexceptionally contain serotonin. This biogenic amine can be demonstrated by the argentaffin reaction of Masson, serotonin immunoreactively or by formalin-induced fluorescence. The characteristic staining pattern of mid-gut carcinoids is almost invariably preserved in the metastatic deposits and consequently the staining methods for identifying serotonin can also be used on metastases to reveal a primary mid-gut carcinoid. The enterochromaffin-like (ECL) cell carcinoids of the body and fundic area of the stomach often seen in association with pernicious anaemia are argyrophil with the Sevier-Munger silver stain. Other neuroendocrine tumours, viz. antral, duodenal and rectal carcinoids should be studied by a battery of relevant peptide hormone antisera for adequate diagnosis. During the last decade new peptide hormones have been found in circulation in patients with carcinoid tumours, but serotonin and urinary 5-HIAA are still the most important markers for carcinoids of the mid-gut origin. Other clinically useful tumour markers are chromogranin A + B, pancreatic polypeptide, human chorionic gonadotropin alpha and beta subunits. For localizing procedures, angiography is the most reliable investigative method for primary tumours in the gut, whereas CT-scan and ultrasound investigations are good for detection of liver metastases. During the last five years, the therapy for malignant carcinoid tumours has been considerably improved. Chemotherapy has only revealed objective response rates in about 10-30% of the patients giving median survivals from start of therapy of about 10 months. Recently treatment with alpha interferons and the new somatostatin analogue octreotide have given objective responses in 50-75% of patients with malignant mid-gut carcinoid tumours. These patients have now a median survival from start of therapy of 70 months when treated with alpha interferons. In the future new therapies will come into use such as monoclonal antibodies and perhaps also agents blocking different growth factors.

Nuclear DNA distribution in neuroendocrine gastroenteropancreatic tumors before and during treatment

The nuclear DNA contents of tumor cells in 73 patients with endocrine gastrointestinal tumors, 19 patients with endocrine pancreatic tumors (EPT) and 54 patients with malignant carcinoid tumors were determined before and after treatment. The DNA profiles were divided into diploid and aneuploid. In untreated patients, 9 out of 10 (90%) primary EPT and all 9 primary malignant carcinoid tumors (100%) were diploid. Tumor cell imprints from liver metastases of patients with untreated EPT showed aneuploidy in 5 of 11 cases, but only in 7 out of 46 DNA records from patients with untreated carcinoid liver metastases. DNA alteration from diploid to aneuploid profiles occurred in 2 patients with endocrine pancreatic tumors who had received chemotherapy. A change from diploid to aneuploid records was also seen in 7/23 (30%) carcinoid tumors after treatment. The DNA patterns before and after treatment did not show any correlation with survival or treatment response.

The influence of hibernation on the interferon response in the spotted suslik (Spermophilus suslicus)

According to the season, the environmental temperature, and their physiological state (whether active or in hibernation), spotted susliks produce different amounts of interferon (IFN) in response to intraperitoneal induction with Newcastle disease virus (NDV). Even though injection of NDV aroused hibernating animals, susliks treated during deep winter hibernation or artificial summer hibernation, or when aroused from winter hibernation, had significantly less IFN in their serum and organs than animals active in summer. Minced tissues taken from such animals and infected with NDV in vitro produced similar relative amounts of IFN. The effects of other environmental factors were studied: IFN production in vivo was increased by a high concentration of CO2 (5%) in the air, but decreased by electric shock stress. A hyporeactive response to IFN induction in vivo was produced in active susliks but not in animals hibernating in summer. These changes in the IFN system associated with season and physiological state cannot be explained merely in terms of the effect of differences in body temperature; they involve also adaptive changes in the animal associated with the onset of hibernation.

Inhibition of mouse bladder tumor proliferation by alpha difluoromethylornithine and interferon in vitro and in vivo

Previous studies have reported that alpha difluoromethylornithine (DFMO), an enzyme-activated, irreversible inhibitor of ornithine decarboxylase (ODC), has anti-tumor activity in several tumor systems. Recently, investigations have revealed that combinations of DFMO and Interferon (IFN) are synergistic in inhibiting tumor cell growth. We tested the effects of DFMO and IFN alpha, beta alone and in combination on the growth of mouse bladder tumor (MBT-2) cells both in vitro and in vivo. MBT-2 cells were incubated for 72 hours in 96 well microtiter plates with DFMO, IFN alpha, beta and combinations of both agents and percentage inhibition was calculated. In vivo studies utilized the intravesical implantation method as well as subcutaneous implantation. DFMO was administered as a 1% solution in the drinking water. IFN alpha, beta was given bi-weekly by intravesical administration. DFMO effectively inhibited MBT-2 growth in vitro. The ID50 was 0.08 mM and peak inhibitory activity was reached at concentrations of 0.16 mM and remained constant with concentrations of up to 10 mM. IFN alpha, beta also inhibited the in vitro proliferation of MBT-2 with maximum inhibition (46%) at 2,000 U/ml. Combinations of DFMO and IFN alpha, beta showed increased anti-proliferative activity. The degree of enhancement varied with synergism, additivity, or sub-additivity at varying drug concentrations. In vivo, DFMO significantly retarded the growth of tumors implanted subcutaneously (p less than .05) and significantly delayed the outgrowth of tumors implanted intravesically (p less than .01). IFN alpha, beta alone was ineffective in vivo and produced no additive effect in vivo when used in combination with DFMO. Results of our investigation show that DFMO inhibits proliferation of MBT-2 cells in vitro and exhibits a similar effect in vivo against subcutaneous and intravesical tumor implants. IFN alpha, beta alone demonstrated anti-proliferative activity in vitro but did not affect MBT-2 growth in vivo. Although the combination of DFMO and IFN alpha, beta exhibited enhanced activity in vitro, no enhancement was observed with combination therapy in vivo.

The biology of interferon actions

The interferons comprise a group of proteins which were first identified by their ability to protect cells against virus infections. They are synthesized and secreted by a variety of cell types in response to various inducers and exert their effects in vivo by interaction with specific cellular receptors. In this sense the interferons are analogous to polypeptide hormones. In recent years it has become clear that the interferons are capable of influencing cellular physiology and behavior in a number of ways. Their effects include antiviral actions, inhibition of cell growth and proliferation, regulation of the expression of specific genes, modulation of cell differentiation and activation of various cell types in the immune system. This review aims to summarize the current state of biology of interferon actions with special emphasis on the hemopoetic system.

Effect of natural beta-interferon on cell proliferation and steroid receptor level in human breast cancer cells

The effect of natural beta-interferon (beta-IFN) on cell proliferation and steroid receptor level was investigated in CG-5 human breast cancer cell line. beta-interferon determines an appreciable diminution of cell growth, at concentrations ranging from 100 to 1000 IU/ml, which is enhanced when serum content of the culture medium is lowered. Low concentrations of beta-IFN (10-100 IU/ml) produce, after a 5-day treatment, an increase in estrogen receptors (ER) and progesterone receptors (PR). No variation of ER and PR levels is observed when beta-IFN is added directly to the cell homogenate before the assay. Our data suggest that beta-IFN could affect hormone sensitivity through a modification of ER and PR in neoplastic mammary cells.

Does successful interferon treatment of tumor patients require life-long treatment?

Case histories of 5 tumor patients treated with natural leukocyte interferon-alpha (IFN-alpha) are presented. One patient with juvenile laryngeal papillomatosis responded well to interferon treatment, but the disease recurred when therapy was withdrawn. Upon reinstitution of treatment, the patient once again responded well. Another patient with myelomatosis also responded well to interferon therapy and in this case, too, the tumor recurred when interferon treatment was withdrawn. Reinstitution of interferon therapy was, however, unsuccessful. One patient with generalized giant cell tumor of bone responded with regression after more than 5 years of interferon treatment. Another patient with pulmonary osteosarcoma metastases, having received irradiation and interferon combination therapy followed by sole interferon treatment, responded well with a lasting stationary radiogram after 6 years of interferon treatment. One patient with malignant glioma, showing signs of tumor growth during the first few months of interferon therapy, eventually responded, and became disease-free after 6 years. The latter 3 patients are continuously receiving interferon therapy although more than 5 years have elapsed since their interferon therapy was initiated. It is suggested that interferon therapy for malignant tumors be given for life (or to progression of disease) in responding patients. Such a concept entails biological implications for interferon therapy in general and for antitumor action of interferons in particular. Other possible clinical schedules should only be constructed within the framework of controlled clinical trials.

Interactions of interferons and transforming growth factors during clonal growth of mouse or human cells in soft agar and in mice

The mouse fibroblast-like transformed cell line C-243 adapted to growth in suspension was used as a source of virus-induced interferons (MulFN-alpha, beta), and spontaneously produced active growth factors. These factors were purified from C-243 cells grown as tumors in BALB/c mice, and had properties identical to those of TGF-alpha or TGF-beta isolated by others from different tissues. Exogenous TGF-alpha, beta stimulated colony formation by C-243 cells in soft agar, whereas MulFN-alpha, beta inhibited it. Clonal growth of human lung adenocarcinoma A549 cells in soft agar was inhibited as well by human interferons (types alpha, beta, or gamma) as by TGF-beta. Inhibition was dose-related. Pure EGF, which is an analogue of TGF-alpha, diminished the antiproliferative activity of interferons alpha, beta, and gamma in A549 cells. On the other hand, the anti-mitogenic action of IFN-beta and TGF-beta was clearly synergistic. In mice bearing C-243 cell tumors, TGF-alpha, beta stimulated growth, whereas MulFN-alpha, beta inhibited it. Stimulation of tumor growth was also observed after administration of anti-IFN serum that could neutralize endogenous IFN-alpha, beta. The simultaneous administration of MulFN-alpha, beta and TGF-alpha, beta diminished anti-tumor effects of IFN in mice. Our results suggest that both TGFs and IFNs are autocrine, positive or negative growth factors modulating the rate of proliferation and the neoplastic behavior of the cells. The final effects depend on the target-cell sensitivity and on the relative concentration of the various hormone-like factors. Cancer cells overstimulated by TGF-alpha, beta or by EGF may not respond to IFNs.

Natural mediators of physiological interferon synthesis

Resident peritoneal cells of BALB/c mice were found to release two types of mediators influencing physiological interferon synthesis, a nondialysable stimulator and a dialysable low molecular inhibitor. The influence of macrophage secreted, biologically active substances on interferon production is discussed. Their participation in the induction of physiological interferons is considered.

Treatment of malignant endocrine pancreatic tumours with human leucocyte interferon

22 patients with advanced malignant endocrine pancreatic tumours were treated with human leucocyte interferon 3-6 X 10(6) IU per day. Objective responses (more than 50% reduction in tumour markers or tumour size) were seen in 7/7 with watery diarrhoea/hypokalaemia/achlorhydria syndrome, 3/4 with the Zollinger-Ellison syndrome, 6/9 with "non-functioning" tumours, and 1 with a mixed tumour mainly producing somatostatin. The median duration of response was 8.5 months, and all responders improved clinically. Adverse effects seemed more tolerable than those of cytotoxic treatment.

A few distinct 'molecular sandwiches' are basis for structural and functional similarities of subspecies of interferon alpha and of families of growth-promoting hormones

'Molecular sandwiches' composed of two aromatic amino acids separated by a hydrophilic one were found on eleven subspecies of human interferon alpha, on murine interferon alpha 2, and human interferon beta 1. In addition, another type of the sandwiches was found on several species of interferon. This confirms and extends the observations concerning the similarities between some interferons and several classical hormones. Furthermore, we are presenting evidence that a distinct type of the 'molecular sandwiches': Tyr-Cys...Cys and/or Cys...Cys-Cys...Cys, that participate in formation of disulfide bonds, is a characteristic marker of most, if not all of the growth-promoting hormones including growth factors. The 'sandwiches' appear to be important for receptor binding.

Down-regulation of peripheral blood cell interferon receptors in chronic myelogenous leukemia patients undergoing human interferon (HuIFN alpha) therapy

Our interest in studying interferon (IFN) receptor activity in peripheral blood cells (PBCs) from patients with chronic myelogenous leukemia (CML) receiving therapeutic doses of partially purified leukocyte IFN (IFN alpha) stems from a need for more adequate monitoring of IFN therapy. The binding of 35S-labelled recombinant DNA-derived leukocyte clone A IFN (35S-rIFN alpha A) to PBCs from 8 patients with CML was determined before and during IFN alpha treatment. The patients' mean pretherapy binding level (0.049 femtomoles of bound 35S-rIFN alpha A) was in the range of values obtained from 4 normal donors (mean of 0.054 femtomoles bound). Within 24 hr of the first IFN alpha dose, the mean femtomoles bound decreased 10-fold and remained low during the course of IFN alpha treatment. In I/I patient, we demonstrated that this decreased binding was due to a loss in number of IFN receptors. The apparent number of receptors after 5 doses of IFN alpha decreased from approximately 600 receptors per cell at pretherapy to approximately 75 receptors per cell, with no difference in the dissociation constants (1.13 X 10(-10)M, 0.968 X 10(-10)M, before and during treatment, respectively). In 4/4 patients, we demonstrated indirectly that the decreased binding was not due to receptor saturation as a result of residual circulating IFN alpha. In 3/3 patients, we demonstrated a gradual recovery of binding capacity after incubating the patients' PBCs at 37 degrees C. Within 2-7 days in vivo recovery of binding, comparable to pretherapy levels, was observed in 3/3 patients whose IFN alpha therapy was discontinued. Combining all these data, we conclude that in both responding and nonresponding patients with CML, IFN alpha exposure induces decreased binding of labelled IFN when a single recombinant DNA-derived IFN species is used. We feel the supporting data indicate that the decreased binding capacity may be due to receptor down-regulation. In the limited number of patients studied thus far, there was no correlation between clinical hematologic response and occurrence of down-regulation, however, down-regulation of cell surface receptors may be required to sustain a biological effect. Further studies of both the kinetics of down-regulation and activation of key enzyme systems are required to fully evaluate the relevance of these findings.

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.

Gamma interferon enhances mitogenic responses induced by pokeweed mitogen

Interferon (IFN)-induced suppression of the lectin-stimulated lymphoproliferative response was studied comparatively with human IFN-alpha, IFN-beta and IFN-gamma, using an equal unit of their antiviral activity ranging from 31.25 to 1000 IU/ml. Both IFN-alpha and IFN-beta inhibited phytohemagglutinin (PHA) and pokeweed mitogen (PWM)-stimulated lymphoblastogenic response similarly in a dose-related fashion, but the IFN-gamma effect was far less. Indeed, the PWM-stimulated lymphocyte blastogenesis in the cultures incubated for 7 days was enhanced in the presence of IFN-gamma at a concentration of 62.5 IU/ml. The enhancing effect was found to be highest at the lowest concentration of IFN-gamma examined. The IFN-gamma induced enhancement of lectin-stimulated blastogenesis was found mainly in the PWM cultures incubated for 7 days but less in cultures incubated for 5 days or in PHA cultures incubated for 3 days, suggesting that the observed effect might be caused by the activation of interleukin production.