IL-22 suppresses the infection of porcine enteric coronaviruses and rotavirus by activating STAT3 signal pathway

Interleukin-22 (IL-22), a member of the IL-10 superfamily, plays essential roles in fighting against mucosal microbial infection and maintaining mucosal barrier integrity within the intestine. However, little knowledge exists on the ability of porcine IL-22 (pIL-22) to fight against viral infection in the gut. In this study, we found that recombinant mature pIL-22 (mpIL-22) inhibited the infection of multiple diarrhea viruses, including alpha coronavirus, porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine rotavirus (PoRV), in the intestinal porcine epithelial cell line J2 (IPEC-J2) cells. mpIL-22 up-regulated the expression of the antimicrobial peptide beta-defensin (BD-2), cytokine IL-18 and IFN-λ. Furthermore, we found that mpIL-22 induced phosphorylation of STAT3 on Ser727 and Tyr705 in IPEC-J2 cells. Inhibition of STAT3 phosphorylation by S3I-201 abrogated the antiviral ability of mpIL-22 and the mpIL-22-induced expression of BD-2, IL-18, and IFN-λ. Together, mpIL-22 inhibited the infection of PoRV and enteric coronaviruses, and up-regulated the expression of antimicrobial genes in IPEC-J2, which were mediated by the activation of the STAT3 signal pathway. The significant antiviral activity of IL-22 to curtail multiple enteric diarrhea viruses in vitro suggests that pIL-22 could be a novel therapeutic against devastating viral diarrhea in piglets.

[ANTIMICROBIAL ACTIVITY OF POLYAZOLIDINAMMONIUM, MODIFIED WITH HYDRATE-IONS OF IODINE]

AIM

Study of antimicrobial activity of a polymer compound--polyazolidinammonium, modified with hydrate-ions of iodine.

MATERIALS AND METHODS

Antimicrobial activity of polyazolidinammonium, modified with hydrate-ions of iodine, against reference strains and clinical isolates of Gram positive and negative bacteria, microscopical fungi, as well as RNA viruses was studied.

RESULTS

High antibacterial activity of the studied compound was established, especially against Gram positive bacteria. A higher concentration of the preparation (125-250 µg/ml) was characterized by anti-fungal effect. A high sensitivity to polymer of swine transmissible gastroenteritis virus was noted.

CONCLUSION

The polymer compound, based on the results of the studies, is a perspective antiseptic and etiotropic means for control of infectious disease causative agents.

Inhibitory effect of silver nanomaterials on transmissible virus-induced host cell infections

Coronaviruses belong to the family Coronaviridae, which primarily cause infection of the upper respiratory and gastrointestinal tract of hosts. Transmissible gastroenteritis virus (TGEV) is an economically significant coronavirus that can cause severe diarrhea in pigs. Silver nanomaterials (Ag NMs) have attracted great interests in recent years due to their excellent anti-microorganism properties. Herein, four representative Ag NMs including spherical Ag nanoparticles (Ag NPs, NM-300), two kinds of silver nanowires (XFJ011) and silver colloids (XFJ04) were selected to study their inhibitory effect on TGEV-induced host cell infection in vitro. Ag NPs were uniformly distributed, with particle sizes less than 20 nm by characterization of environmental scanning electron microscope and transmission electron microscope. Two types of silver nanowires were 60 nm and 400 nm in diameter, respectively. The average diameter of the silver colloids was approximately 10 nm. TGEV infection induced the occurring of apoptosis in swine testicle (ST) cells, down-regulated the expression of Bcl-2, up-regulated the expression of Bax, altered mitochondrial membrane potential, activated p38 MAPK signal pathway, and increased expression of p53 as evidenced by immunofluorescence assays, real-time PCR, flow cytometry and Western blot. Under non-toxic concentrations, Ag NPs and silver nanowires significantly diminished the infectivity of TGEV in ST cells. Moreover, further results showed that Ag NPs and silver nanowires decreased the number of apoptotic cells induced by TGEV through regulating p38/mitochondria-caspase-3 signaling pathway. Our data indicate that Ag NMs are effective in prevention of TGEV-mediated cell infection as a virucidal agent or as an inhibitor of viral entry and the present findings may provide new insights into antiviral therapy of coronaviruses.

Transmissible gastroenteritis virus: identification of M protein-binding peptide ligands with antiviral and diagnostic potential

The membrane (M) protein is one of the major structural proteins of coronavirus particles. In this study, the M protein of transmissible gastroenteritis virus (TGEV) was used to biopan a 12-mer phage display random peptide library. Three phages expressing TGEV-M-binding peptides were identified and characterized in more depth. A phage-based immunosorbent assay (phage-ELISA) capable of differentiating TGEV from other coronaviruses was developed using one phage, phTGEV-M7, as antigen. When the phage-ELISA was compared to conventional antibody-based ELISA for detecting infections, phage-ELISA exhibited greater sensitivity. A chemically synthesized, TGEV-M7 peptide (pepTGEV-M7; HALTPIKYIPPG) was evaluated for antiviral activity. Plaque-reduction assays revealed that pepTGEV-M7 was able to prevent TGEV infection in vitro (p<0.01) following pretreatment of the virus with the peptide. Indirect immunofluorescence and real-time RT-PCR confirmed the inhibitory effects of the peptide. These results indicate that pepTGEV-M7 might be utilized for virus-specific diagnostics and treatment.

Action mechanisms of lithium chloride on cell infection by transmissible gastroenteritis coronavirus

Transmissible gastroenteritis virus (TGEV) is a porcine coronavirus. Lithium chloride (LiCl) has been found to be effective against several DNA viruses, such as Herpes simplex virus and vaccinia virus. Recently, we and others have reported the inhibitory effect of LiCl on avian infectious bronchitis coronavirus (IBV) infection, an RNA virus. In the current study, the action mechanism of LiCl on cell infection by TGEV was investigated. Plaque assays and 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenyl tetrazoliumbromide (MTT) assays showed that the cell infection by TGEV was inhibited in a dose-dependent manner, when LiCl was added to virus-infected cells; the cell infection was not affected when either cells or viruses were pretreated with the drug. The inhibition of TGEV infection in vitro by LiCl was observed at different virus doses and with different cell lines. The inhibitory effect of LiCl against TGEV infection and transcription was confirmed by RT-PCR and real-time PCR targeting viral S and 3CL-protease genes. The time-of-addition effect of the drug on TGEV infection indicated that LiCl acted on the initial and late stage of TGEV infection. The production of virus was not detected at 36 h post-infection due to the drug treatment. Moreover, immunofluorescence (IF) and flow cytometry analyses based on staining of Annexin V and propidium iodide staining of nuclei indicated that early and late cell apoptosis induced by TGEV was inhibited efficiently. The ability of LiCl to inhibit apoptosis was investigated by IF analysis of caspase-3 expression. Our data indicate that LiCl inhibits TGEV infection by exerting an anti-apoptotic effect. The inhibitory effect of LiCl was also observed with porcine epidemic diarrhea coronavirus. Together with other reports concerning the inhibitory effect of lithium salts on IBV in cell culture, our results indicate that LiCl may be a potent agent against porcine and avian coronaviruses.

Putative probiotic Lactobacillus spp. from porcine gastrointestinal tract inhibit transmissible gastroenteritis coronavirus and enteric bacterial pathogens

A total of 310 bacterial strains isolated from the porcine gastrointestinal tract were tested for their activity against transmissible gastroenteritis (TGE) coronavirus and other enteric pathogens. Based on activity, the strains Probio-38 and Probio-37 were selected as potential probiotics and identified as Lactobacillus plantarum Probio-38 and Lactobacillus salivarius Probio-37 respectively by 16S rRNA gene sequencing. Supernatants of these strains inhibited TGE coronavirus in vitro in ST cells, without any cytopathic effect even after 72 h of incubation. Both the strains exhibited high survival in synthetic gastric juice. The strains were resistant to 5% porcine bile and exhibited antimicrobial activity against all the 13 enteric bacterial pathogens tested. These strains also exhibited resistance to most of the antibiotics analyzed. The inhibition of transmissible gastroenteritis coronavirus and enteric bacterial pathogens as well as the bile tolerance, high survival in gastric juice, and the antibiotic resistance indicate that the two isolated bacterial strains are ideal probiotic candidates for animal application after proper in vivo experiments.

Identification of phenanthroindolizines and phenanthroquinolizidines as novel potent anti-coronaviral agents for porcine enteropathogenic coronavirus transmissible gastroenteritis virus and human severe acute respiratory syndrome coronavirus

The discovery and development of new, highly potent anti-coronavirus agents and effective approaches for controlling the potential emergence of epidemic coronaviruses still remains an important mission. Here, we identified tylophorine compounds, including naturally occurring and synthetic phenanthroindolizidines and phenanthroquinolizidines, as potent in vitro inhibitors of enteropathogenic coronavirus transmissible gastroenteritis virus (TGEV). The potent compounds showed 50% maximal effective concentration (EC₅₀) values ranging from 8 to 1468 nM as determined by immunofluorescent assay of the expression of TGEV N and S proteins and by real time-quantitative PCR analysis of viral yields. Furthermore, the potent tylophorine compounds exerted profound anti-TGEV replication activity and thereby blocked the TGEV-induced apoptosis and subsequent cytopathic effect in ST cells. Analysis of the structure-activity relations indicated that the most active tylophorine analogues were compounds with a hydroxyl group at the C14 position of the indolizidine moiety or at the C3 position of the phenanthrene moiety and that the quinolizidine counterparts were more potent than indolizidines. In addition, tylophorine compounds strongly reduced cytopathic effect in Vero 76 cells induced by human severe acute respiratory syndrome coronavirus (SARS CoV), with EC₅₀ values ranging from less than 5 to 340 nM. Moreover, a pharmacokinetic study demonstrated high and comparable oral bioavailabilities of 7-methoxycryptopleurine (52.7%) and the naturally occurring tylophorine (65.7%) in rats. Thus, our results suggest that tylophorine compounds are novel and potent anti-coronavirus agents that may be developed into therapeutic agents for treating TGEV or SARS CoV infection.

Novel small-molecule inhibitors of transmissible gastroenteritis virus

We used swine testicle (ST) cells infected with transmissible gastroenteritis virus (TGEV) and an indirect immunofluorescent assay with antibodies against TGEV spike and nucleocapsid proteins to screen small-molecule compounds that inhibit TGEV replication. Analogues of initial hits were collected and subjected to a 3CL protease (3CL(pro)) inhibition assay with recombinant 3CL(pro) and a fluorogenic peptide substrate. A series of benzothiazolium compounds were found to have inhibitory activity against TGEV 3CL(pro) and to exert anti-TGEV activities in terms of viral protein and RNA replication in TGEV-infected ST cells, with consequent protection of TGEV-infected ST cells from cytopathic effect by blocking the activation of caspase-3.

Identifying inhibitors of the SARS coronavirus proteinase

The Severe Acute Respiratory Syndrome (SARS) is a serious respiratory illness that has recently been reported in parts of Asia and Canada. In this study, we use molecular dynamics (MD) simulations and docking techniques to screen 29 approved and experimental drugs against the theoretical model of the SARS CoV proteinase as well as the experimental structure of the transmissible gastroenteritis virus (TGEV) proteinase. Our predictions indicate that existing HIV-1 protease inhibitors, l-700,417 for instance, have high binding affinities and may provide good starting points for designing SARS CoV proteinase inhibitors.

Sialic acid binding activity of transmissible gastroenteritis coronavirus affects sedimentation behavior of virions and solubilized glycoproteins

The sedimentation behavior of transmissible gastroenteritis coronavirus (TGEV) was analyzed. Upon sucrose gradient centrifugation, the major virus band was found at a density of 1.20 to 1.22 g/cm(3). This high density was observed only when TGEV with a functional sialic acid binding activity was analyzed. Mutants of TGEV that lacked sialic acid binding activity due to a point mutation in the sialic acid binding site of the S protein were mainly recovered at a lower-density position on the sucrose gradient (1.18 to 1.19 g/cm(3)). Neuraminidase treatment of purified virions resulted in a shift of the sedimentation value from the higher to the lower density. These results suggest that binding of sialoglycoproteins to the virion surface is responsible for the sedimentation behavior of TGEV. When purified virions were treated with octylglucoside to solubilize viral glycoproteins, ultracentrifugation resulted in sedimentation of the S protein of TGEV. However, when neuraminidase-treated virions or mutants with a defective sialic acid binding activity were analyzed, the S protein remained in the supernatant rather than in the pellet fraction. These results indicate that the interaction of the surface protein S with sialoglycoconjugates is maintained after solubilization of this viral glycoprotein by detergent treatment.

Downstream ribosomal entry for translation of coronavirus TGEV gene 3b

Gene 3b (ORF 3b) in porcine transmissible gastroenteritis coronavirus (TGEV) encodes a putative nonstructural polypeptide of 27.7 kDa with unknown function that during translation in vitro is capable of becoming a glycosylated integral membrane protein of 31 kDa. In the virulent Miller strain of TGEV, ORF 3b is 5'-terminal on mRNA 3-1 and is presumably translated following 5' cap-dependent ribosomal entry. For three other strains of TGEV, the virulent British FS772/70 and Taiwanese TFI and avirulent Purdue-116, mRNA species 3-1 is not made and ORF 3b is present as a non-overlapping second ORF on mRNA 3. ORF 3b begins at base 432 on mRNA 3 in Purdue strain. In vitro expression of ORF 3b from Purdue mRNA 3-like transcripts did not fully conform to a predicted leaky scanning pattern, suggesting ribosomes might also be entering internally. With mRNA 3-like transcripts modified to carry large ORFs upstream of ORF 3a, it was demonstrated that ribosomes can reach ORF 3b by entering at a distant downstream site in a manner resembling ribosomal shunting. Deletion analysis failed to identify a postulated internal ribosomal entry structure (IRES) within ORF 3a. The results indicate that an internal entry mechanism, possibly in conjunction with leaky scanning, is used for the expression of ORF 3b from TGEV mRNA 3. One possible consequence of this feature is that ORF 3b might also be expressed from mRNAs 1 and 2.

Antiviral effect of trimeric 2',5'-oligoadenylic acid and some of its analogues

The antiviral effect of 2',5'-trioligoadenylate (2',5'-A3) and some of its analogues was studied using several model cell culture systems and viruses: mice L929 fibroblast cells inoculated with vaccine virus, testicular piglet cells inoculated with Aueszki disease virus (strain BUK-628), and the same culture inoculated with a reference strain of transmissible gastroenteritis virus, strain Purdue-115. Our results suggest that both 2',5'-trioligoadenylate and its analogues are promising antiviral substances against DNA- and RNA-containing viruses.

Antiviral action of interferon-alpha against porcine transmissible gastroenteritis virus

Swine testis (ST) cell cultures were treated with various doses of recombinant human interferon-alpha 2a (IFN), and assayed for 2',5' oligoadenylate synthetase (2-5 A synthetase) activity. Treatment with 100 or 1000 units/ml of IFN resulted in increased 2-5 A synthetase activity, but there was no significant response to 1 unit/ml of IFN. Titres of porcine transmissible gastroenteritis virus (TGEV) were reduced between 6 and 15 hours post-infection in ST cells treated with 1000 or 2500 units/ml of IFN. Polyacrylamide gel electrophoresis of lysates of TGEV-infected ST cells, and of lysates immunoprecipitated with anti-TGEV antibodies, revealed that the synthesis of the N and S proteins of TGEV was reduced in cells treated with 100 or 1000 units/ml of IFN. Viral RNA production, as determined with a probe which hybridized to the S gene of TGEV, was found to be reduced in ST cells treated with 1000 units/ml of IFN, but not in cells treated with 100 units/ml. It was concluded that, in IFN-treated ST cells, TGEV protein production may be decreased in the absence of reduced viral RNA production, and that 2-5 A synthetase may not be a significant factor in the antiviral activity of IFN against TGEV.

Antiviral activity of interferon against transmissible gastroenteritis virus in cell culture and ligated intestinal segments in neonatal pigs

Segments of jejunum in 5 to 6 days old piglets were surgically ligated, inoculated with transmissible gastroenteritis virus (TGEV) and 18 hours later the segments were fixed for histology or suspensions were prepared for plaque assay in swine testis (ST) cell cultures to determine the yield of virus. When the virulent Purdue strain of TGEV was used, villous atrophy was seen and TGEV antigen was demonstrated immunohistochemically in the villous enterocytes. The Miller M6 strain of virus produced less extensive lesions in the segments, but since it was titratable by plaque assay it was used in the subsequent yield reduction assays to determine the antiviral activity of interferon. When intestinal segments were inoculated simultaneously with either 3200 units of natural porcine interferon-alpha or up to 1000,000 units of recombinant human interferon-alpha 2 a, and TGEV, there no reductions in virus yield, although the same cytokines exerted an antiviral effect in ST cells treated in a similar way. However, virus yields were significantly reduced in intestinal segments in piglets treated parenterally with the synthetic interferon inducer polyinosinic: polycytidylic acid 6 hours before challenge of the segments with TGEV. There was also a trend for the antiviral effects of interferon induction before challenge to be augmented by the inclusion of interferon with the virus inoculum. It was concluded that interferon would be ineffective as a therapeutic for TGEV, although it might be useful prophylactically.

Inhibition of appearance of pH-dependent virus-cell fusion by neutralizing monoclonal antibodies to transmissible gastroenteritis virus

Five MAbs, which showed neutralizing (NT) activity and recognized S (previously designated E2) glycoprotein of TGE virus TO-163, inhibited cell fusion by TGE virus in IB-RS-2 cells. Other S-specific MAbs with no NT activity did not inhibit the cell fusion. The results indicate that a neutralization epitope is same or very close to a fusion active site. The kinetics of membrane fusion following a reduction in pH were also investigated. The cell fusion appeared between 2 and 6 hr after the binding medium was added.

The multiplication of transmissible gastroenteritis viruses in several cell lines originated from porcine kidney and effects of trypsin on the growth of the viruses

Plaque formation, replication and related cytopathic function of 9 strains of transmissible gastroenteritis (TGE) virus were examined in primary cells and cell lines such as CPK, IB-RS-2, ESK, and PK-15 originated from porcine kidney and the effects of trypsin on the replication of TGE virus were examined in CPK cells. All strains produced a cytopathic effect and grew well in CPK cells as well as in primary porcine kidney cells. The effect of trypsin on the plaque formation was different from strains. The number of plaques produced by strains TO-163, Ukiha and Niigata increased from 2.6 to 3.52 times when trypsin was present in the medium during incubation at 37 degrees C for 1 hr after adsorption of the virus at 4 degrees C for 2 hr. The plaque sizes of TO-163, h-5, Ukiha and Niigata became larger from 1.4 to 1.7 times, when trypsin was present in the agar MEM overlay.

[Isolation of a concentrated purified preparation of the transmissible gastroenteritis virus of swine and a study of its antigenic properties]

Pretreatment of the transmissible gastroenteritis virus of swine (TGE) (coronavirus) with trypsin increased the yield of the infectious virus approximately 100-fold when propagated in roller cultures of SPEV cells, the time required for the development of marked CPE being twice shorter than without treatment. The method of concentration and purification of TGE virus is described which yields a preparative amount of highly purified virions retaining their structure. Such preparations were used for immunization of guinea pigs. It is concluded that purified preparations of TGE virus possess marked antigenic potency and may be used for generation of highly active and specific hyperimmune sera.

Transmissible gastroenteritis (TGE) of swine: in vitro virus attachment and effects of polyanions and polycations

Four transmissible gastroenteritis virus (TGEV) strains (Purdue-115, D-52, 188-SG and Gep-II) and two cell lines (swine testis-ST and pig kidney-RPD) were used to study virus attachment and cell susceptibility. Virus attachment was partially thermodependent and the rate varied, depending on the strain. Identical TGEV inocula produced a higher plaque number by plaque assay in the swine testis cell line (ST) than in the pig kidney cell line (RPD) but [3H]uridine-labelled virus was found associated equally well with both cell lines. A field TGEV strain (Gep-II), which was unable to multiply in cell cultures, appeared able to inhibit the attachment of radiolabelled cell-passaged virus. Therefore, the susceptibility to TGEV infection was apparently not determined at the virus-to-cell attachment stage. The attachment sites on the cell surface were specific, however, differences in TGEV attachment determinant between strains were not observed. Attachment of all the virus strains tested was enhanced by DEAE-dextran and inhibited by dextran sulfate, poly-L-lysine (PLL), poly-L-alpha-ornithine (PLO) and protamine sulfate.

A double-protease-resistant variant of transmissible gastroenteritis virus and its ability to induce lactogenic immunity

A virus resistant to 2 major intestinal proteases (trypsin and alpha-chymotrypsin) was derived from the attenuated Purdue strain of transmissible gastroenteritis virus. Its enzymatic stability was confirmed, in vitro, by exposure to proteolytic enzymes and to porcine intestinal fluids. Vaccination of 5 seronegative pregnant sows with the variant virus by a series of 2 oral and 1 IM inoculations resulted in high titers of neutralizing antibody in serum and colostrum. The mean antibody titer in milk whey decreased 44-fold within 1 week after parturition. At 3 days of age, the 40 pigs delivered by these sows were challenge exposed orally with virulent transmissible gastroenteritis virus. Pigs nursing the 5 vaccinated sows underwent a relatively mild clinical course of illness. The average mortality of these 40 pigs was 33%. Thirty-six pigs which had been raised by 4 nonvaccinated sows had a more severe illness, greater daily weight loss, and higher mortality (92%).

Influence of infectivity of transmissible gastroenteritis virus of swine by pancreatin and some unknown factors

The infectivity of virulent strain, not attenuated strain, of transmissible gastroenteritis virus (TGEV) of swine could be enhanced as much as 50-fold by pancreatin incorporated medium. The mechanism(s) of enhancement was uncertained. Multiplication of TGEV, either virulent or attenuated strain, was inhibited by intestinal fluid of both TGEV infected and noninfected piglets. Pelleting virus particles from intestine fluid was likely to remove all inhibitors and resulted in facilitating the isolation of the virus by using swine testicle (ST) cell line. These findings contribute to the practical application in the isolation and identification of TGEV and in the preparation of high titred virus stocks.

Laboratory evaluation of selected disinfectants as virucidal agents against porcine parvovirus, pseudorabies virus, and transmissible gastroenteritis virus

Of a variety of disinfectants evaluated, only sodium hypochlorite and sodium hydroxide inactivated porcine parvovirus (PPV) after a 5-minute incubation period. After the same incubation time, pseudorabies and transmissible gastroenteritis viruses were inactivated by all of the disinfectants tested. When the incubation time was increased to 20 minutes, 2% glutaraldehyde and a double-strength concentration of a commercial formaldehyde preparation also inactivated PPV. Formaldehyde vapor and ultraviolet radiations inactivated PPV also, but relatively long exposure times were required.

[Inhibiting activity of amantadine (1-aminoadamantane) on the transmissible gastroenteritis virus of swine in cell cultures]

Studies were carried out on the inhibiting activity of amantadine - 1-amino adamantine (1-AA) on the virus of swine transmissive gastroenteritis, Rakovski strain, in cell cultures of pig kidney and thyroid gland. The inhibiting agent was tested in concentration of 6.25 to 100 microgram/cm3. Parallel titrations with and without 1-AA (25, 50, and 100 microgram/cm3) were used to establish the maximum difference in the titers 2 lg. The effect of inhibition was manifested at minimum concentration of 1-AA (12.5 microgram/cm3), and increased up to a concentration of 100 microgram/cm3. Within the interval 12.5-25.00-50.00 microgram/cm3 the doubling of the concentration of the inhibitor led to the decrease in the virus titer by 1 lg. In experiments to follow up the dynamics of the virus growth in the course of four days with and without 1-AA at the rate of 100 microgram/cm3 at varying multiplicity of infecting (from 0.5 up to 0.00005) the transient differences between the titers rose to 4.5 lg, while the differences between the peak values of the titer rose up to 2.5 lg. By means of seven consecutive passage of two variants of the virus selected by their decrease or increase in sensitivity to the inhibiting agent no change in their sensitivity to 1-AA was achieved.