Interferon inducers protect mice against plasmodium berghei malaria

Hepatocytes and the art of killing Plasmodium softly

The Plasmodium parasites that cause malaria undergo asymptomatic development in the parenchymal cells of the liver, the hepatocytes, prior to infecting erythrocytes and causing clinical disease. Traditionally, hepatocytes have been perceived as passive bystanders that allow hepatotropic pathogens such as Plasmodium to develop relatively unchallenged. However, now there is emerging evidence suggesting that hepatocytes can mount robust cell-autonomous immune responses that target Plasmodium, limiting its progression to the blood and reducing the incidence and severity of clinical malaria. Here we discuss our current understanding of hepatocyte cell-intrinsic immune responses that target Plasmodium and how these pathways impact malaria.

SARS-CoV-2 decreases malaria severity in co-infected rodent models

Coronavirus disease 2019 (COVID-19) and malaria, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Plasmodium parasites, respectively, share geographical distribution in regions where the latter disease is endemic, leading to the emergence of co-infections between the two pathogens. Thus far, epidemiologic studies and case reports have yielded insufficient data on the reciprocal impact of the two pathogens on either infection and related diseases. We established novel co-infection models to address this issue experimentally, employing either human angiotensin-converting enzyme 2 (hACE2)-expressing or wild-type mice, in combination with human- or mouse-infective variants of SARS-CoV-2, and the P. berghei rodent malaria parasite. We now show that a primary infection by a viral variant that causes a severe disease phenotype partially impairs a subsequent liver infection by the malaria parasite. Additionally, exposure to an attenuated viral variant modulates subsequent immune responses and provides protection from severe malaria-associated outcomes when a blood stage P. berghei infection was established. Our findings unveil a hitherto unknown host-mediated virus-parasite interaction that could have relevant implications for disease management and control in malaria-endemic regions. This work may contribute to the development of other models of concomitant infection between Plasmodium and respiratory viruses, expediting further research on co-infections that lead to complex disease presentations.

Type I Interferons and Malaria: A Double-Edge Sword Against a Complex Parasitic Disease

Type I interferons (IFN-Is) are important cytokines playing critical roles in various infections, autoimmune diseases, and cancer. Studies have also shown that IFN-Is exhibit 'conflicting' roles in malaria parasite infections. Malaria parasites have a complex life cycle with multiple developing stages in two hosts. Both the liver and blood stages of malaria parasites in a vertebrate host stimulate IFN-I responses. IFN-Is have been shown to inhibit liver and blood stage development, to suppress T cell activation and adaptive immune response, and to promote production of proinflammatory cytokines and chemokines in animal models. Different parasite species or strains trigger distinct IFN-I responses. For example, a Plasmodium yoelii strain can stimulate a strong IFN-I response during early infection, whereas its isogenetic strain does not. Host genetic background also greatly influences IFN-I production during malaria infections. Consequently, the effects of IFN-Is on parasitemia and disease symptoms are highly variable depending on the combination of parasite and host species or strains. Toll-like receptor (TLR) 7, TLR9, melanoma differentiation-associated protein 5 (MDA5), and cyclic GMP-AMP synthase (cGAS) coupled with stimulator of interferon genes (STING) are the major receptors for recognizing parasite nucleic acids (RNA/DNA) to trigger IFN-I responses. IFN-I levels in vivo are tightly regulated, and various novel molecules have been identified to regulate IFN-I responses during malaria infections. Here we review the major findings and progress in ligand recognition, signaling pathways, functions, and regulation of IFN-I responses during malaria infections.

Effects of type I interferons in malaria

Type I interferons (IFNs) are a family of cytokines with a wide range of biological activities including anti-viral and immune-regulatory functions. Here, we focus on the protozoan parasitic disease malaria, and examine the effects of type I IFN-signalling during Plasmodium infection of humans and experimental mice. Since the 1960s, there have been many studies in this area, but a simple explanation for the role of type I IFN has not emerged. Although epidemiological data are consistent with roles for type I IFN in influencing malaria disease severity, functional proof of this remains sparse in humans. Several different rodent-infective Plasmodium species have been employed in in vivo studies of parasite-sensing, experimental cerebral malaria, lethal malaria, liver-stage infection, and adaptive T-cell and B-cell immunity. A range of different outcomes in these studies suggests a delicately balanced, multi-faceted and highly complex role for type I IFN-signalling in malaria. This is perhaps unsurprising given the multiple parasite-sensing pathways that can trigger type I IFN production, the multiple isoforms of IFN-α/β that can be produced by both immune and non-immune cells, the differential effects of acute versus chronic type I IFN production, the role of low level 'tonic' type I IFN-signalling, and that signalling can occur via homodimeric IFNAR1 or heterodimeric IFNAR1/2 receptors. Nevertheless, the data indicate that type I IFN-signalling controls parasite numbers during liver-stage infection, and depending on host-parasite genetics, can be either detrimental or beneficial to the host during blood-stage infection. Furthermore, type I IFN can promote cytotoxic T lymphocyte immune pathology and hinder CD4⁺ T helper cell-dependent immunity during blood-stage infection. Hence, type I IFN-signalling plays highly context-dependent roles in malaria, which can be beneficial or detrimental to the host.

Comparison of the effects of a synthetic polyribonucleotide with the effects of endotoxin on selected host responses

An injection of a small dose (1 to 50 mug) of synthetic polyriboinosinic acid complexed with polyribocytidylic acid (poly I:poly C) inhibited the induction of tryptophan oxygenase by cortisone acetate; it induced tyrosine amino transferase, and it accelerated the loss of liver glycogen reserves. It also resulted in first a suppression followed by an activation of the reticuloendothelial system as judged by the rates of carbon clearance from blood. All of these responses are elicited by comparable doses of endotoxin. Pretreatment of mice with poly I:poly C did not, or only marginally, increased their nonspecific resistance to infection with several bacterial pathogens, and it failed to result in the development of tolerance to endotoxin, effects known to be produced by endotoxin when given under similar conditions.

Protection of mice against bacterial infection by interferon inducers

Antibacterial effect of known interferon inducers was investigated. Intraperitoneal injection of statolon or pyran markedly enhanced the survival of mice challenged with Klebsiella pneumoniae. The sparing effect of these two interferon inducers resembled that of bacterial endotoxin. Significant protection was obtained when the inducers were administered 24 hr before challenge. Treatments given 6 hr before or at the time of infection were ineffective. The persistence of increased resistance of treated animals to encephalomyocarditis virus strain MM, inoculated 5 days after challenge with K. pneumoniae, indicated that the bacterial infection did not adversely influence the induction or effectiveness of interferon.

Effect of Interferon and Interferon Inducers on Infections with a Nonviral Intracellular Microorganism, Rickettsia akari

The effect of mouse interferon (IF) on the multiplication of Rickettsia akari in homologous (L-929) cell cultures and the effect of IF inducers on R. akari infection in mice were investigated. There was a reduction in the proportion of cells containing rickettsiae in IF-treated cultures and in the yield of rickettsiae from these cultures, as compared with those from infected cultures without IF. Trypsin treatment and heating for 1 hr at 65 C destroyed this antirickettsial activity of the IF preparation, whereas ultracentrifugation (105,000 x g for 90 min) and acidification at pH 2.0 did not affect it. There was no evidence that mouse IF inactivated R. akari directly, nor did it have an inhibitory effect on multiplication of R. akari in heterologous chick embryo cell or monkey kidney cell cultures. Susceptibility of R. akari to the action of IF was about 16 times less than that of Chlamydia trachomatis and 256 times less than the susceptibility of vesicular stomatitis virus. Mice were not protected from infection with R. akari by intraperitoneal injection with IF inducers, Newcastle disease virus (10(8.3) plaque-forming units/0.2 ml) or polyriboinosinic acid-polyribocytidylic acid complex (poly I:C, 200 mug/0.2 ml), within 24 hr before or 24 hr after intraperitoneal challenge. The yields of R. akari harvested from the spleens, livers, and peritoneal washings of infected mice treated with IF inducers were similar to those of infected control mice. Titers of IF in peritoneal washings of treated mice, taken 6 hr after administration of Newcastle disease virus or 9 hr after injection of poly I:C, were 1,024 or 320 units/ml, respectively.

Effects of Dextran Sulfate 500 on Cell-Mediated Resistance to Infection with Listeria monocytogenes in Mice

Injection of dextran sulfate 500 caused loss of antibacterial resistance. Mice became more susceptible to an infection with Listeria monocytogenes and were unable to develop antilisterial immunity after both active and passive immunization with passively administered spleen cells from Listeria-immune donors. Indirect evidence suggests that the phagocytic component of cell-mediated resistance to bacterial infection is the site of attack of dextran sulfate.

Kupffer cells are obligatory for Plasmodium yoelii sporozoite infection of the liver

Previous studies suggested Plasmodium sporozoites infect hepatocytes after passing through Kupffer cells, but proof has been elusive. Here we present new information strengthening that hypothesis. We used homozygous op/op mice known to have few Kupffer cells because they lack macrophage colony stimulating factor 1 required for macrophage maturation due to a deactivating point mutation in the osteopetrosis gene. We found these mice to have 77% fewer Kupffer cells and to exhibit reduced clearance of colloidal carbon particles compared with heterozygous phenotypically normal littermates. Using a novel quantitative reverse transcription polymerase chain reaction assay for P. yoelii 18S rRNA, we found liver infection of op/op mice to be decreased by 84% compared with controls. However, using another way of limiting Kupffer cells, treatment with liposome-encapsulated clodronate, infection of normal mice was enhanced seven- to 15-fold. This was explained by electron microscopy showing temporary gaps in the sinusoidal cell layer caused by this treatment. Thus, Kupffer cell deficiency in op/op mice decreases sporozoite infection by reducing the number of portals to the liver parenchyma, whereas clodronate increases sporozoite infection by opening portals and providing direct access to hepatocytes. Together these data provide strong support for the hypothesis that Kupffer cells are the portal for sporozoites to hepatocytes and critical for the onset of a malaria infection.

The role of type I interferons in non-viral infections

For a long time, the family of type I interferons (IFN-alpha/beta) has received little attention outside the fields of virology and tumor immunology. In recent years, IFN-alpha/beta regained the interest of immunologists, due to the phenotypic and functional characterization of IFN-alpha/beta-producing cells, the definition of novel immunomodulatory functions and signaling pathways of IFN-alpha/beta, and the observation that IFN-alpha/beta not only exerts antiviral effects but is also relevant for the pathogenesis or control of certain bacterial and protozoan infections. This review summarizes the current knowledge on the production and function of IFN-alpha/beta during non-viral infections in vitro and in vivo.

Concomitant infections, parasites and immune responses

Concomitant infections are common in nature and often involve parasites. A number of examples of the interactions between protozoa and viruses, protozoa and bacteria, protozoa and other protozoa, protozoa and helminths, helminths and viruses, helminths and bacteria, and helminths and other helminths are described. In mixed infections the burden of one or both the infectious agents may be increased, one or both may be suppressed or one may be increased and the other suppressed. It is now possible to explain many of these interactions in terms of the effects parasites have on the immune system, particularly parasite-induced immunodepression, and the effects of cytokines controlling polarization to the Th1 or Th2 arms of the immune response. In addition, parasites may be affected, directly or indirectly, by cytokines and other immune effector molecules and parasites may themselves produce factors that affect the cells of the immune system. Parasites are, therefore, affected when they themselves, or other organisms, interact with the immune response and, in particular, the cytokine network. The importance of such interactions is discussed in relation to clinical disease and the development and use of vaccines.

Inhibition of Plasmodium yoelii blood-stage malaria by interferon alpha through the inhibition of the production of its target cell, the reticulocyte

The effect of a recombinant hybrid human interferon alpha (IFN-alpha) (which cross-reacts with murine cells) on C57BL/6 mice infected with Plasmodium yoelii sporozoites or parasitized erythrocytes was determined. IFN-alpha did not inhibit the development of the parasite in the liver, but it did reduce the blood parasite load and the hepatosplenomegaly induced by the infection in mice injected with blood-stage parasites. The extent of anemia in IFN-alpha-treated and control mice was similar, despite the lower parasite load in the IFN-alpha-treated mice. The reduced blood parasite load in IFN-alpha-treated mice was associated with reduced erythropoiesis and reticulocytosis. As reticulocytes are the preferred target cells for the strain of P yoelii used (P yoelii yoelii 265 BY), it was postulated that the inhibition of reticulocytosis in IFN-alpha-treated mice was causally related to the observed decreased blood parasite load. This was supported by the finding that IFN-alpha inhibited a different strain of P yoelii (17X clone A), which also displays a tropism for reticulocytes, but not a line of Plasmodium vinckei petteri, which infects only mature red blood cells. As human malaria species also display different tropism for reticulocytes, these findings could be relevant for people coinfected with multiple Plasmodium species or strains or coinfected with Plasmodium and virus. (Blood. 2001;97:3966-3971)

Babesia bovis immunity. In vitro and in vivo evidence for IL-10 regulation of IFN-gamma and iNOS

IL-10 has been shown to have profound immunoregulatory attributes and in the bovine appears to downregulate both Th1- and Th2-like responses. Using RT-PCR, we demonstrate IL-10 in vitro down-regulation of mRNA expression of iNOS, the cytokines involved in nitric oxide signal transduction initiation (IFN-gamma and TNF-alpha), and other mononuclear phagocyte associate cytokines. In addition, using RT-PCR with peripheral blood leukocytes and spleen leukocytes, the Griess reaction, and a killing assay, we provide evidence for the importance of iNOS in a successful immune response to B. bovis infection and for high and persistent IL-10 mRNA expression when the immune response is unsuccessful. We also provide evidence that antibody developed early after an initial infection appears to lack protective attributes (neutralizing and opsonic). Together, the data suggests that IL-10 and IFN-gamma are critical molecules involved in the response to this intraerythrocytic protozoan infection.

Interleukin-12 in infectious diseases

Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that is crucially involved in a wide range of infectious diseases. In several experimental models of bacterial, parasitic, viral, and fungal infection, endogenous IL-12 is required for early control of infection and for generation and perhaps maintenance of acquired protective immunity, directed by T helper type 1 (Th1) cells and mediated by phagocytes. Although the relative roles of IL-12 and gamma interferon in Th1-cell priming may be to a significant extent pathogen dependent, common to most infections is that IL-12 regulates the magnitude of the gamma interferon response at the initiation of infection, thus potentiating natural resistance, favoring Th1-cell development; and inhibiting Th2 responses. Treatment of animals with IL-12, either alone or as a vaccine adjuvant, has been shown to prevent disease by many of the same infectious agents, by stimulating innate resistance or promoting specific reactivity. Although IL-12 may enhance protective memory responses in vaccination or in combination with antimicrobial chemotherapy, it is yet unclear whether exogenous IL-12 can alter established responses in humans. Continued investigation into the possible application of IL-12 therapy to human infections is warranted by the role of the cytokine in inflammation, immunopathology, and autoimmunity.

Porcine interferon-gamma inhibits the growth of Legionella pneumophila in WiREF cells in vitro

The intracellular growth of Legionella pneumophila in WiREF (Wistar rat embryonal fibroblast) cells was inhibited by porcine interferon-gamma. The effect was compared with that of different human interferons (alpha and gamma). The growth inhibition was dose-dependent and required the pretreatment of WiREF cells with interferon. The development of an antibacterial state of the cells was observed. When interferon was added together with bacteria or 1 d after the infection there was no inhibition. Also, there was no direct antibacterial effect of the interferon. In addition, cell pretreatment with a combination of interferon and antibiotics failed to show a synergistic effect.

Poly ICLC inhibits Plasmodium cynomolgi B malaria infection in rhesus monkeys

Prophylatic treatment with a single dose of 1.0 or 2.0 mg/kg (body weight) of polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (Poly ICLC), a potent interferon (IFN) inducer and immune enhancer, 18 h before intravenous inoculation of sporozoites (1.04 x 10(5)-0.70 x 10(6) sporozoites) of Plasmodium cynomolgi B in the rhesus monkey, completely abolished the infectivity of sporozoites. The inhibitory effect of Poly ICLC is dose dependent in monkeys infected with P. cynomolgi B sporozoites. Treatment with lower doses of Poly ICLC (0.5 mg/kg) provided significant protection, but the lowest dose of Poly ICLC used (0.1 mg/kg) failed to provide any protection. Prophylactic treatment with Poly ICLC, however, had no protective effect against trophozoite-induced infection.

Production of interferon-gamma during infection of mice with Plasmodium chabaudi chabaudi

An ELISA assay, designed to detect interferon-gamma (IFN-gamma) in the picogram range, was used to study the presence of IFN-gamma in serum and its production by T cells taken from C57BL/6 mice infected with Plasmodium chabaudi chabaudi. IFN-gamma was detectable in mouse plasma for two to three days before the peak of parasitaemia. Similarly, IFN-gamma production by T cells could be detected in vitro. In limiting dilution cultures, the production of IFN-gamma by as few as 1,000 T cells was detectable using this assay. The limiting dilution analysis revealed that a substantial IFN-gamma response by specific T cells occurs very early in a primary infection with P. chabaudi.

Recombinant human gamma interferon inhibits simian malaria

Prophylactic treatment with 0.1 mg of human gamma interferon per kg (body weight) per day completely suppressed experimental infection with Plasmodium cynomolgi B sporozoites in rhesus monkeys. Treatment with lower doses partially suppressed this infection. Prophylactic treatment with human gamma interferon, however, had no protective effect against trophozoite-induced infection, suggesting that the interferon effect was limited to the exoerythrocytic stage of parasitic development.

Inhibition of development of exoerythrocytic forms of malaria parasites by gamma-interferon

A specific DNA probe was used to study the effect of recombinant rat, mouse, and human gamma-interferon (gamma-IFN) on the course of sporozoite-induced malaria infections. In mice and rats infected with sporozoites of Plasmodium berghei, mouse and rat gamma-IFN's strongly inhibited the development of the exoerythrocytic forms in the liver liver cells of the hosts, but not the development of the erythrocytic stages. The degree of inhibition of the exoerythrocytic forms was proportional to the dose of gamma-IFN administered, but was independent of the number of sporozoites used for challenge. A 30 percent reduction in the development of exoerythrocytic forms in rat liver was achieved when 150 units (about 15 nanograms of protein) of rat gamma-IFN were injected a few hours before sporozoite challenge; the reduction was 90 percent or more with higher doses of gamma-IFN. The effect was less pronounced if the gamma-IFN was administered 18 hours before or a few hours after challenge. Human gamma-IFN also diminished the parasitemia in chimpanzees infected with sporozoites of the human malaria parasite Plasmodium vivax. The target of gamma-IFN activity may be the infected hepatocytes themselves, as shown by in vitro experiments in which small doses of the human lymphokine inhibited the development of exoerythrocytic forms of Plasmodium berghei in a human hepatoma cell line. These results suggest that immunologically induced interferon may be involved in controlling malaria infection under natural conditions.

Interferon inhibits the growth of Legionella micdadei in mouse L cells

The intracellular growth of Legionella micdadei was inhibited in mouse L cells treated with interferon (IFN). This IFN-mediated restriction was dose-dependent and required preincubation of the L cells with high doses of IFN (1,000 U/ml) for maximal inhibition. Incubation of L. micdadei with IFN alone had no detectable effect on growth of the bacteria. The IFN-mediated growth restriction was not dependent upon tryptophan concentration in the culture medium.

Protection of athymic (Nu/Nu) BALB/c mice against Plasmodium berghei by splenocytes from normal (Nu/+) BALB/c mice

Athymic BALB/c (Nu/Nu) mice died at 7-13 days after inoculation (DAI) of Plasmodium berghei NK65, whereas their heterozygous (Nu/+) littermates died at 7-8 DAI. Nude (Nu/Nu) mice, reconstituted with 2 x 10(7) splenocytes from uninfected heterozygous (Nu/+) littermates at 20 days before parasite inoculation (DBI), died about 2 days earlier than control nude mice; nude mice reconstituted at 10 or 2 DBI lived 2 to 4 days longer than control nudes; and nude mice reconstituted 2 DAI lived even longer and some survived. These findings indicate that P. berghei NK65 induces at least two T-cell dependent immune phenomena, one suppressive and the other stimulatory. Reconstitution of nude mice with T-cells from BALB/c (Nu/+) mice appeared to reduce or bypass suppressive T-cell activities which allowed the formation of a protective immune response by some of the nude mice.

Mouse fibroblast interferon modifies Salmonella typhimurium infection in infant mice

The effect of mouse fibroblast interferon on Salmonella typhimurium infection in infant mice was examined. The lethality to mice that had been given S. typhimurium intragastrically was significantly reduced in a dose-dependent manner when the mice were pretreated with fibroblast interferon. Lower doses of interferon delayed the development of disease. Interferon neutralized with anti-interferon globulin did not influence the lethality of S. typhimurium to mice. In mice treated with interferon there was also a reduced invasiveness of S. typhimurium in intestinal epithelial cells in vivo. It was further demonstrated in an in vitro system that interferon pretreatment of mouse L-929 cells inhibited the invasiveness of the bacteria in a dose-dependent manner. The in vitro inhibition was neutralized with anti-interferon globulin. The results indicate that interferon inhibits Salmonella bacteria from invading cells and establishing an intracellular state of infection. This may represent an important factor in the pathogenesis of disease.

Effect of human leukocyte interferon on invasiveness of Salmonella species in HEp-2 cell cultures

The effect of human leukocyte interferon on the invasiveness of Salmonella and Shigella species in HEp-2 cell cultures was examined. The intracellular and extracellular bacteria were identified by a combination of Nomarski differential interference contrast microscopy and UV incident light microscopy applied on the same microscope. Pretreatment of HEp-2 cells with human leukocyte interferon reduced the number of Salmonella typhimurium and Salmonella paratyphi-B bacteria per cell and the proportion of cells containing bacteria in a dose-dependent manner. Maximum inhibitory effect was observed with ca. 100 U of interferon per ml. The inhibitory effect was neutralized with anti-human interferon globulin. Murine fibroblast interferon did not influence the invasiveness of Salmonella species. Invasiveness of Shigella flexneri was not influenced by treatment of cells with human interferon.

Immunopotentiation against internal parasites

The economic importance of livestock losses attributed to internal parasites has led to the need of developing and successfully employing effective antiparasitic vaccines. An increasingly important strategy in the development of more effective vaccines is the preparation and use of immunopotentiators or adjuvants. Immunopotentiators or adjuvants have been used effectively in combination with antigen(s) or alone to protect animals against internal parasites. The use of immunopotentiators for specific and nonspecific stimulation of protective immunity against internal parasites is reviewed.

The effects of selective immunosuppression on resistance to Mesocestoides corti in strains of mice showing high and low initial susceptibility

Previous work has shown that C57BL/6 mice had the lowest initial susceptibility to Mesocestoides corti of six strains of mice examined. Parasite burdens in this strain and in CBA/H mice, a strain showing a higher initial susceptibility to M. corti, were compared following selective immunosuppressive treatments. Irradiation, splenectomy and the administration of cyclophosphamide and methyl prednisolone all resulted in higher parasite burdens in C57BL/6 mice. In contrast these treatments had a minimal effect on parasite burdens in CBA/H mice. In the light of these results the role of antibody in controlling parasite proliferation is discussed.

Interferon: an inducer of macrophage activation by polyanions

Purified mouse fibroblast interferon (IF) directly rendered resting macrophages tumoricidal. The physicochemical properties and species specificity of the stimulatory agent fall within the present definition of IF. Since a number of polyanions induce macrophage IF, the antitumor and antimicrobial activities may result from the ability of newly released IF to modify macrophage activity.

Influence of 9-beta-D-arabinofuranosyladenine on total protein synthesis and on differential gene expression of unique proteins in the rodent malarial parasite Plasmodium berghei

The antibiotic 9-beta-D-arabinofuranosyladenine is a drug with a broad spectrum of activity against animal viruses, with little or no effect on mammalian cells, when administered in vivo or in vitro. Here we report that the antibiotic markedly inhibited the incorporation of [35S]methionine into malarial protein. Inhibition was apparent when the parasites were either exposed to the drug in vivo during the course of infection or incubated with the drug in vitro. Moreover, the antibiotic induced pronounced changes in the spectrum of proteins synthesized. Some proteins that are prominently apparent in the control disappear from the drug-treated parasites; others specific for drug-treated parasites appear, indicating changes in the commitment for gene expression as manifested by the appearance of the final protein product. Proteins synthesized were analyzed by two-dimensional polyacrylamide gels; the first dimension used isoelectric focusing in cylinder gels and the second dimension used electrophoresis in a lithium dodecyl sulfate slab gel. Proteins were visualized by radioautography.

Antiviral activity and induction of interferon-like substance by quinacrine and acranil

Several drugs with certain structural similarities (tricyclic ring system with dialkylaminoalkyl side chains) to tilorone, a potent interferon inducer, were screened for antiviral activity in vivo. Two acridine drugs, Acranil and quinacrine, were found to be effective, the former being almost as protective as tilorone and the latter less so. Both agents induced an interferon-like substance which could be detected in the serum of treated mice. The concentration of the inhibitory factor in the serum was highest after exposure to tilorone, followed in turn by Acranil and quinacrine, based on the administration of equal weights of drugs. Both tilorone and Acranil induced lower levels of circulating interferon-like substance in Balb/c mice than in other strains of mice. The serum factor induced by Acranil was shown to be stable at pH 2.

Nonspecific protective action against Vibrio cholerae of SK&F 42319, a ribonucleic acid obtained from bacteriophage-infected Escherichia coli

An interferon-inducing RNA, SK&F 42319, obtained from a lysate of phage-infected Escherichia coli, protected mice against Vibrio cholerae infection. This nonspecific protection was not attributable to endotoxin contamination.

Suppression of the intracellular growth of Shigella flexneri in cell cultures by interferon preparations and polyinosinic-polycytidylic acid

A strain of Shigella flexneri type 2a was found to multiply intracellularly in cultures of the diploid human cell strain FS-1 and in secondary rabbit kidney cells. When inoculated cultures were stained and observed under the light microscope, it appeared that the cytoplasm of infected cells became gradually filled with bacteria. Various preparations of human and rabbit interferon were found to suppress the intracellular bacterial growth in homologous cells. Polyinosinic-polycytidylic acid (poly I.poly C) had a similar inhibitory effect. Rabbit interferon preparations did not cause a significant suppression in human cells. Suppression of the bacterial growth could be demonstrated in two ways: (i) by showing that treatment with either homologous interferon or poly I.poly C reduced the proportion of infected cells determined by counting the total number of cells and the number of cells with 10 or more bacteria in several microscopic fields selected at random, or (ii) by showing that a suppression in (3)H-uridine incorporation by bacteria occurs in infected cultures treated with actinomycin D after incubation with interferon or poly I.poly C. (Uridine incorporation by the bacterium is insensitive to actinomycin D.) Treatment of cells with actinomycin D before incubation with interferon prevented the development of cellular resistance to bacterial infection. Interferon preparations did not have an inhibitory effect on the extracellular growth of S. flexneri in a broth culture. These findings show that the range of activity of the interferon system apparently extends to intracellularly growing bacteria.

Enhancement of phagocytosis by interferon-containing preparations

Exposure of mononuclear cells from the mouse peritoneal cavity to interferon (IF)-containing mouse sera enhanced phagocytosis of colloidal carbon particles by the cells. The same effect was observed when the cells were exposed to IF-containing cell culture harvest free of serum. The magnitude of this effect of IF-containing preparations paralleled the titer of IF and was not related to the dilution of various IF-containing serum specimens tested. The factor responsible for the enhancing effect was stable at pH 2, inactivated by trypsin, and nonsedimentable at 105,000 x g. Heating at 60 C for 1 hr destroyed it, and its kinetics of heat inactivation paralleled that of the antiviral activity of IF. A period of incubation of phagocytic cells with IF-containing serum was necessary before a maximum level of enhancement was reached, and once established was not removable by repeated washing of cells. The kinetics of the production of the enhancing factor in mice injected with Newcastle disease virus was essentially identical to that of the simultaneous production of IF as measured by antiviral activity. Contrary to the effect of mouse IF preparations, human IF preparation did not enhance the activity of mouse phagocytes. It appears, therefore, that the phagocytosis-enhancing factor falls within the present definition of IF.

The effect of an interferon inducer on Eimeria maxima in the chicken

The intraperitoneal inoculation of chickens with 100–170 mg of Statolon, an artificial interferon inducer in mammals, induced the production of a virus interference factor in the serum. Chickens, 3 and 5 weeks old given 40–170 mg Statolon i.p. produced significantly fewer oocysts after infection withE. maximathan untreated chickens.

Only three serum samples (from a large number examined) taken from chickens 1, 4 or 6 days afterE. tenellainfection or 6 h and 6 days afterE. maximainfection showed slight but significant antiviral effects.