Cytopathic Effects In Infected Cells Research Articles

Isolation and Genomic Characterization of SARS-CoV-2 Omicron Variant Obtained from Human Clinical Specimens.

Due to the failure of virus isolation of the Omicron variant in Vero CCL-81 from the clinical specimens of COVID-19 cases, an initial in vivo and subsequent in vitro approach was utilized for the isolation of the virus. A total of 74 oropharyngeal/nasopharyngeal specimens were collected from SARS-CoV-2 positive international travellers and a contact case at Delhi and Mumbai, India. All the specimens were sequenced using next-generation sequencing and simultaneously inoculated onto Vero CCL-81 cells for virus isolation. Subsequently, two omicron positive specimens were inoculated into Syrian hamsters for two passages. The initial passage of the positive hamster specimens was inoculated onto Vero CCL-81 cells. The clinical specimens, hamster specimens, and Vero CCL-81 passages were sequenced to assess the mutational changes in different host species. The replication of the Omicron variant in hamsters was confirmed with the presence of a high viral load in nasal turbinate and lung specimens of both passages. The successful isolation of the virus from hamster specimens with Vero CCL-81 was observed with cytopathic effect in infected cells and high viral load in the cell suspension. The genome analysis revealed the presence of L212C mutation, Tyrosine 69 deletion, and C25000T nucleotide change in spike gene of hamster passage sequences and an absence of V17I mutation in E gene in hamster passage sequences, unlike human clinical specimen and Vero CCL-81 passages. No change was observed in the furin cleavage site in any of the specimen sequences, suggesting intact pathogenicity of the virus isolate. Our data demonstrated successful isolation of the Omicron variant with the in vivo method first followed by in vitro method. The virus isolate could be used in the future to explore different aspects of the Omicron variant.

Apoptosis mechanisms induced by parvovirus infections.

Parvoviruses affect both vertebrates and invertebrates, and can be both detrimental and benign to the host. Numerous studies about parvovirus-induced apoptotic cell death have been researched and reported. In most parvovirus infections, cell death heightens the virus dissemination and causes tissue damage, often leading to disease. Cell cycle arrest also induces cytopathic effects in infected cells and is sometimes aprerequisite to apoptotic cell death. Cell death mechanisms caused by parvovirus infections vary depending on the infecting parvovirus strain and the cell lines involved. Apo-ptosis, however, is afrequent form of cell death induced by parvoviruses. The non-structural protein 1 (NS1) is amajor contributor to parvovirus infection-induced cell death. However, other proteins such as the 11kDa, NP1 and viral genome replication can also induce cell death. Understanding the mechanisms involved in parvovirus cell death, and host response is important in the development of treatment for cytopathic parvoviruses. This review article discusses parvovirus-induced apoptotic cell death and the mechanisms involved. Keywords: apoptosis; cell cycle arrest; cell death; parvovirus; viral protein.

African pygmy hedgehog adenovirus: Virus replication, virus-induced cytopathogenesis and activation of mitogen-activated protein kinase signaling pathways in infected MDCK cells

We examined several aspects of African hedgehog adenovirus (AhAdv-1) that was isolated from an African pygmy hedgehog, including: replication kinetics of, virus-induced cytopathic effect (CPE), activation status of mitogen-activated protein kinase (MAPK) signaling pathways, and possible roles of these signaling pathways in virus replication and virus-induced CPE in MDCK cells. AhAdv-1 efficiently replicated and induced CPE in infected cells and caused accumulation of cleaved caspase-3 at 24 h post-infection (p.i.), suggesting apoptosis induction. Analysis of several intracellular signal transduction pathways, which are involved in apoptosis, showed activation of p38 MAPK, Akt and ERK1/2 pathways at 3 h p.i., and upregulation of phosphorylated SAPK/JNK at 24 h p.i. Although p38 MAPK inhibitor and SAPK/JNK inhibitor suppressed activation of the respective pathways in infected cells, they did not inhibit virus-induced CPE. Treatment of infected cells with inhibitor of the Akt pathway, the p38 pathway, the SAPK/JNK pathway or the ERK pathway revealed that inhibitors of p38 pathway inhibited viral replication by real-time PCR and TCID50 assay in infected MDCK cells, suggesting that AhAdv-1 uses p38 pathway for multiplication in infected cells.

Isolation of a highly pathogenic spring viraemia of carp virus strain from grass carp (Ctenopharyngodon idella) in late summer, China, 2016

Spring viraemia of carp virus (SVCV) is an OIE-listed notifiable pathogen, which has brought huge economic loss to the aquaculture industry. Outbreaks of SVC mostly occur in spring with water temperature 11–17°C. Presently, there is an increase in detection during import quarantine testing and associated with outbreaks of SVCV outside of China, yet China is regarded as the origin of SVCV Asian clade. However, recent isolates from the Shanghai area all showed to be low pathogenic to their original hosts. In this study, we isolated a new SVCV strain (nominated as SH160901) from grass carp in late summer in Shanghai, 2016. Phylogenetic analysis showed this strain formed a distinct new lineage in the Asian clade along with our isolate SH150514 in 2015, and was divergent from all other identified Asian isolates. Cell infection test demonstrated that this strain replicated most efficiently at 25°C and 28°C, and could induce obvious cytopathic effect in infected cells. In vivo infection test revealed this strain could cause severe symptoms in experimentally infected fish at 16–20°C. Inoculated fish died at 100% in grass carp and common carp (Cyprinus carpio carpio) within 13days, and at 100% in goldfish (Carassius auratus) and 90% in koi (Cyprinus carpio koi) within 40days. Experimental infections at 26°C also induced moderate mortalities in grass carp (25%) and common carp (20%). The biological changes characterized for SVCV isolate SH160901 warrant changes to surveillance plans, specifically there is a need to broaden the testing parameters previously associated with SVCV.

Mycoplasma agalactiae Induces Cytopathic Effects in Infected Cells Cultured In Vitro.

Mycoplasma agalactiae is the etiological agent of the contagious agalactia syndrome in sheep and goats and causes significant economic losses worldwide. Yet the mechanism of pathogenesis is largely unknown. Even whole-genome sequence analysis of its pathogenic type strain did not lead to any conclusions regarding its virulence or pathogenicity factors. Although inflammation and tissue destruction at the local site of M. agalactiae infection are largely considered as effects of the host immune response, the direct effect of the agent on host cells is not completely understood. The aim of this study was to investigate the effect of M. agalactiae infection on the quality and viability of host cells in vitro. Changes in cell morphology including cell elongation, cytoplasm shrinkage and membrane blebbing were observed in infected HeLa cells. Chromatin condensation and increased caspase-3 cleavage in infected HeLa cells 48 h after infection suggests an apoptosis-like phenomenon in M. agalactiae-infected cells. In compliance with these results, decreased viability and cell lysis of M. agalactiae-infected HeLa cells was also observed. Measurement of the amount of LDH released after M. agalactiae infection revealed a time- and dose-dependent increase in HeLa cell lysis. A significant decrease in LDH released after gentamicin treatment of infected cells confirmed the major role of cytadherent M. agalactiae in inducing host cell lysis. This is the first study illustrating M. agalactiae’s induction of cytopathic effects in infected HeLa cells. Further detailed investigation of infected host tissue for apoptotic markers might demonstrate the association between M. agalactiae-induced host cell lysis and the tissue destruction observed during M. agalactiae natural infection.

Negative effect of heat shock on feline calicivirus release from infected cells is associated with the control of apoptosis

FCV infection causes rapid cytopathic effects, and its replication results in the induction of apoptosis changes in cultured cells. It is well established that the survival of apoptotic cells can be enhanced by the expression of heat-shock proteins (Hsp) to prevent damage or facilitate recovery. Hsps can act as molecular chaperones, but they can also have anti-apoptotic roles by binding to apoptotic proteins and inhibiting the activation of caspases, the primary mediators of apoptosis. Because apoptosis occurs during FCV infection and heat shock (HS) treatment has a cytoprotective role due to the expression of Hsps, we studied the effect of the HS response to hyperthermia during FCV infection in cultured cells. We found that FCV infection does not inhibit the expression of Hsp70 induced by HS and that non-structural and structural protein synthesis was not modified during HS treatment. However, HS caused a delay in the appearance of a cytopathic effect in infected cells, as well as a reduction in the extracellular but not in the cell-associated viral yield. This antiviral effect of HS correlates with the inhibition of caspase-3 activation. Thus, the HS-induced reduction in virus production appeared to be associated with the control of apoptosis, supporting previous data that indicate that apoptosis is necessary for FCV release.

Construction, characterization and immunogenicity of a glycoprotein E negative bovine herpesvirus-1.1 Egyptian strain “Abu-Hammad”

A full glycoprotein E (gE) deletion was generated in genome of the Egyptian BoHV-1.1 Abu-Hammad strain. Integrity of the gE negative (gE−) mutant virus was proved by successful specific PCR amplifications of gB, gC, tk, gD, gI and gE genes along with definite immune reaction to polyclonal anti-BoHV-1 antibody in infected cell culture. BoHV-1 gE− mutant exhibited growth kinetics inferior to those of the parental virus manifested as lower virus titers with delayed and poorer cytopathic effect in infected cells. Adjuvanted vaccines were made of the gE− mutant, live and killed; besides a conventional killed vaccine made of the parental virus and were used to immunize separate groups of calves. After i.m. vaccinations, no virus shedding could be detected in nasal swabs collected from all vaccinates and all calves remained apparently healthy. They all seroconverted to BoHV-1 as was revealed by virus neutralization test and a gB enzyme-linked immunosorbent assay (ELISA). Calves vaccinated with live and killed gE− vaccines did not elicit any detectable anti-gE antibody as shown by a blocking gE-ELISA. In conclusion, the constructed BoHV-1.1 gE− mutant was proved as safe and immunogenic as a reliable candidate for inclusion in a local marker vaccine.

Quantitative in vivo and in vitro characterization of co-infection by two genetically distant grass carp reoviruses

Grass carp reovirus (GCRV) is one of the most serious pathogens threatening grass carp (Ctenopharyngodon idella) production in China. Through sequence analysis, the co-existence of two genetically distant grass carp reoviruses, named GCRV-JX01 and GCRV-JX02, was revealed in the same diseased grass carp sample collected in 2011. GCRV-JX01 and GCRV-JX02 shared high levels of homology with GCRV-873 and GCRV-GD108, respectively. In contrast to GCRV-JX01, GCRV-JX02 induced no cytopathic effect in infected cells. A quantitative real-time PCR assay was employed to monitor the replication efficiency of both virus strains in either Ctenopharyngodon idella kidney (CIK) cells or infected cell supernatant. The results demonstrated that, although GCRV-JX02 did reduce the cellular replication level of GCRV-JX01 up to 10-fold during co-infection, there was no significant impact on the productive virus progeny level in supernatant compared to that of cells infected by GCRV-JX01 alone. To validate the hypothesis that both viruses might co-infect grass carp without significant interference in the field, we collected clinical samples from two different fish farms in 2012 and monitored virus loads for each fish. The data showed that 55% of the collected fish samples were co-infected by GCRV-JX01 and GCRV-JX02, and the single virus infection rate was 10% for GCRV-JX01 and 20% for GCRV-JX02. For both viruses, the in vivo viral loads under co-infection and single viral infection were similar. No serological cross-reaction or cross-protection occurred between GCRV-JX01 and JX02 in our immunization and challenge tests. This new information on co-infection by two genetically distant virus strains should be helpful for designing vaccines targeting the causative agents of grass carp haemorrhagic disease.

Construction and Preparation of Three Recombinant Adenoviruses Expressing Truncated NS3 and Core Genes of Hepatitis C Virus for Vaccine Purposes

BackgroundIn spite of dozens of clinical trials to establish effective therapeutic and/or preventive vaccine to resolve HCV infection, no real vaccine has been proved to date. Genetic vaccines based on replication-defective adenoviruses have proved to elicit strong and long lasting T-cell responses against a number of viral antigens and are even currently being used for vaccine trials in humans. According to the controversy in the immune modulatory effects of both core and NS3 full length genes, it seemed more practical to employ some parts of these HCV proteins for vaccine design.ObjectivesTo generate recombinant Adenoviral vectors containing new overlapping-truncated region of NS3 gene or both the N- and C-terminal deleted parts of core gene, as well as a fusion fragment derived from both of them.Materials and MethodsThe corresponding transfer vectors expressing truncated fragments of core, NS3 or a fusion fragment of both genes were prepared. The integrity and sequence of the transfer vectors were confirmed, and followed by experiments involving homologous recombination between them and the adenovirus backbone plasmid in the bacterial host. Recombinant Ad-pNS3, Ad-pCore and Ad-pNS3pCore viruses were prepared by transfection of these new recombined constructs into 293 packaging cell lines. The virus titer was then calculated by an immunohistochemistry based method. The RT-PCR, Real-Time PCR and western blotting were used to evaluate gene expression by all recombinant constructs. The production of complete virion particles was evaluated by detailed electron microscopy in addition to the appearance of typical cytopathic effects (CPE) and GFP expression patterns in 293 cells. The RT-PCR and GFP detection were employed to monitor the integrity as well as infectivity potency of the viral particles in Hep-G2 cells.ResultsRT-PCR, Real-Time PCR or western blotting confirmed expression of truncated fragment of NS3, core or a fusion fragment of theirs by newly constructed Ad-pNS3, Ad-pCore, Ad- pNS3pCore particles. Electron microscopy, which revealed many adenovirus-like particles and characteristics of CPE in infected cells in addition to GFP detection, confirmed the infectivity, potency and integrity of recombinant adenoviral particles.ConclusionsThese adenoviruses expressing novel fragments of NS3 and core genes may be suitable tools to overcome shortcomings associated with full gene expression in the setting of HCV vaccine therapy.

Receptor-bound porcine epidemic diarrhea virus spike protein cleaved by trypsin induces membrane fusion

Porcine epidemic diarrhea virus (PEDV) infection in Vero cells is facilitated by trypsin through an undefined mechanism. The present study describes the mode of action of trypsin in enhancing PEDV infection in Vero cells during different stage of the virus life cycle. During the viral entry stage, trypsin increased the penetration of Vero-cell-attached PEDV by approximately twofold. However, trypsin treatment of viruses before receptor binding did not enhance infectivity, indicating that receptor binding is essentially required for trypsin-mediated entry upon PEDV infection. Trypsin treatment during the budding stage of virus infection induces an obvious cytopathic effect in infected cells. Furthermore, we also show that the PEDV spike (S) glycoprotein is cleaved by trypsin in virions that are bound to the receptor, but not in free virions. These findings indicate that trypsin affects only cell-attached PEDV and increases infectivity and syncytium formation in PEDV-infected Vero cells by cleavage of the PEDV S protein. These findings strongly suggest that the PEDV S protein may undergo a conformational change after receptor binding and cleavage by exogenous trypsin, which induces membrane fusion.

Mixed Lineage Kinase 3 deficiency delays viral clearance in the lung and is associated with diminished influenza-induced cytopathic effect in infected cells

Influenza virus leads to acute respiratory disease resulting in seasonal epidemics and periodic pandemics. Little is known about the signaling events that regulate host defense to influenza. One particular pathway, the c-Jun amino-terminal kinase (JNK) cascade is activated following influenza infection and blocking JNK leads to enhanced viral replication. We hypothesize that Mixed Lineage Kinase 3 (MLK3), an upstream regulator of JNK, is involved in the host response to influenza. To test this, wild-type and MLK3-/- mice were infected with pathogenic strain of influenza A virus, A/PR/8/34 (PR8). Although, cellular and humoral immune responses were similar between wild-type and MLK3-/- hosts, the viral load in the lungs was comparatively higher in MLK3-/- mice at day 8 post-infection. Consistent with this, MLK3-/- murine lung fibroblast and epithelial cells had prolonged survival and increased virion production following infection compared to wild-type. These findings support a role for MLK3 in viral production during influenza infection.

Newcastle disease virus-induced cytopathic effect in infected cells is caused by apoptosis

The velogenic Newcastle disease virus (NDV) causes highly infectious and economically significant Newcastle disease (ND) in birds of various species. In cell culture NDV induces cytopathic effect (CPE) characterized by rounding, vacuolation, syncytia formation and cell death. Aside from cell to cell fusion caused by the F and HN glycoprotein of the virus molecular events leading to cell death are not known. In the current study, NDV-infected Vero cells, at 48 h p.i., showed nuclear condensation, cytoplasm blebbing, DNA fragmentation, and phosphatidylserine translocation to the cell surface. In addition, virus-infected cells demonstrated decreased DNA content and an increased Bax to Bcl-2 ratio, p53 level and caspase 3, 8, 9 expression compared to mock-infected cells. Based on these results, it was concluded that CPE in NDV-infected cells was caused by to the induction of apoptosis with the involvement of p53 and the Bax, dependent apoptotic pathways.

Ribavirin treatment up-regulates antiviral gene expression via the interferon-stimulated response element in respiratory syncytial virus-infected epithelial cells.

Respiratory syncytial virus (RSV) is a mucosa-restricted virus that is a leading cause of epidemic respiratory tract infections in children. RSV replication is a potent activator of the epithelial-cell genomic response, influencing the expression of a spectrum of cellular pathways, including proinflammatory chemokines of the CC, CXC, and CX(3)C subclasses. Ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) is a nontoxic antiviral agent currently licensed for the treatment of severe RSV lower respiratory tract infections. Because ribavirin treatment reduces the cytopathic effect in infected cells, we used high-density microarrays to investigate the hypothesis that ribavirin modifies the virus-induced epithelial genomic response to replicating virus. Ribavirin treatment administered in concentrations of 10 to 100 micro g/ml potently inhibited RSV transcription, thereby reducing the level of RSV N transcripts to approximately 13% of levels in nontreated cells. We observed that in both the absence and the presence of ribavirin, RSV infection induced global alterations in the host epithelial cell, affecting approximately 49% of the approximately 6,650 expressed genes detectable by the microarray. Ribavirin influences the expression of only 7.5% of the RSV-inducible genes (total number of genes, 272), suggesting that the epithelial-cell genetic program initiated by viral infection is independent of high-level RSV replication. Hierarchical clustering of the ribavirin-regulated genes identified four expression patterns. In one group, ribavirin inhibited the expression of the RSV-inducible CC chemokines MIP-1 alpha and -1 beta, which are important in RSV-induced pulmonary pathology, and interferon (IFN), a cytokine important in the mucosal immune response. In a second group, ribavirin further up-regulated a set of RSV- and IFN-stimulated response genes (ISGs) encoding antiviral proteins (MxA and p56), complement products, acute-phase response factors, and the STAT and IRF transcription factors. Because IFN-beta expression itself was reduced in the ribavirin-treated cells, we further investigated the mechanism for up-regulation of the IFN-signaling pathway. Enhanced expression of IFI 6-16, IFI 9-27, MxA/p78, STAT-1 alpha, STAT-1 beta, IRF-7B, and TAP-1-LMP2 transcripts were independently reproduced by Northern blot analysis. Ribavirin-enhanced TAP-1-LMP2 expression was a transcriptional event where site mutations of the IFN-stimulated response element (ISRE) blocked RSV and ribavirin-inducible promoter activity. Furthermore, ribavirin up-regulated the transcriptional activity of a reporter gene selectively driven by the ISRE. In specific DNA pull-down assays, we observed that ribavirin enhanced RSV-induced STAT-1 binding to the ISRE. We conclude that ribavirin potentiates virus-induced ISRE signaling to enhance the expression of antiviral ISGs, suggesting a mechanism for the efficacy of combined treatment with ribavirin and IFN in other chronic viral diseases.

Antiviral effects of pyrrolidine dithiocarbamate on human rhinoviruses.

Human rhinoviruses (HRVs) are the predominant cause of the common cold. The frequency of HRV infections in industrial countries and the lack of effective therapeutical treatment underline the importance of research for new antiviral substances. As viral infections are often accompanied by the generation of oxidative stress inside the infected cells, several redox-active substances were tested as potential antivirals. In the course of these studies it was discovered that pyrrolidine dithiocarbamate (PDTC) is an extremely potent compound against HRV and poliovirus infection in cell culture. Besides the ability to dramatically reduce HRV production by interfering with viral protein expression, PDTC promotes cell survival and abolishes cytopathic effects in infected cells. PDTC also protects cells against poliovirus infection. These effects were highly specific, as several other antioxidants (vitamin C, Trolox, 2-mercaptoethanol, and N-acetyl-L-cysteine) are inactive against HRV infection. Synthesis of HRV proteins and cleavage of eucaryotic initiation factor 4G responsible for host cell shutoff of cellular protein synthesis are severely inhibited in the presence of PDTC.

Ectopic gene expression and homeotic transformations in arthropods using recombinant Sindbis viruses

The morphological diversity of arthropods makes them attractive subjects for studying the evolution of developmental mechanisms. Comparative analyses suggest that arthropod diversity has arisen largely as a result of changes in expression patterns of genes that control development. Direct analysis of how a particular gene functions in a given species during development is hindered by the lack of broadly applicable techniques for manipulating gene expression. We report that the Arbovirus Sindbis can be used to deliver high levels of gene expression in vivo in a number of non-host arthropod species without causing cytopathic effects in infected cells or impairing development. Using recombinant Sindbis virus, we investigated the function of the homeotic gene Ultrabithorax in the development of butterfly wings and beetle embryos. Ectopic Ultrabithorax expression in butterfly forewing imaginal discs was sufficient to cause the transformation of characteristic forewing properties in the adult, including scale morphology and pigmentation, to those of the hindwing. Expression of Ultrabithorax in beetle embryos outside of its endogenous expression domain affected normal development of the body wall cuticle and appendages. The homeotic genes have long been thought to play an important role in the diversification of arthropod appendages. Using recombinant Sindbis virus, we were able to investigate homeotic gene function in non-model arthropod species. We found that Ultrabithorax is sufficient to confer hindwing identity in butterflies and alter normal development of anterior structures in beetles. Recombinant Sindbis virus has broad potential as a tool for analyzing how the function of developmental genes has changed during the diversification of arthropods.

Membrane permeabilization by small hydrophobic nonstructural proteins of Japanese encephalitis virus.

Infection with Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, may cause acute encephalitis in humans and induce severe cytopathic effects in various types of cultured cells. We observed that JEV replication rendered infected baby hamster kidney (BHK-21) cells sensitive to the translational inhibitor hygromycin B or alpha-sarcine, to which mock-infected cells were insensitive. However, little is known about whether any JEV nonstructural (NS) proteins contribute to virus-induced changes in membrane permeability. Using an inducible Escherichia coli system, we investigated which parts of JEV NS1 to NS4 are capable of modifying membrane penetrability. We found that overexpression of NS2B-NS3, the JEV protease, permeabilized bacterial cells to hygromycin B whereas NS1 expression failed to do so. When expressed separately, NS2B alone, but not NS3, was sufficient to alter bacterial membrane permeability. Similarly, expression of NS4A or NS4B also rendered bacteria susceptible to hygromycin B inhibition. Examination of the effect of NS1 to NS4 expression on bacterial growth rate showed that NS2B exhibited the greatest inhibitory capability, followed by a modest repression from NS2A and NS4A, whereas NS1, NS3, and NS4B had only trivial influence with respect to the vector control. Furthermore, when cotransfected with a reporter gene luciferase or beta-galactosidase, transient expression of NS2A, NS2B, and NS4B markedly reduced the reporter activity in BHK-21 cells. Together, our results suggest that upon JEV infection, these four small hydrophobic NS proteins have various modification effects on host cell membrane permeability, thereby contributing in part to virus-induced cytopathic effects in infected cells.

Human immunodeficiency virus type 1 Vpu modifies viral cytopathic effect through augmented virus release.

We characterized two human immunodeficiency virus type 1 (HIV-1) strains, HIVMCK and HIV213, which have different cytopathic effects in infected cells. HIV213 was highly cytopathic, whereas HIVMCK was not. Biological analyses of chimeric viruses from the cloned infectious DNAs of HIVMCK and HIV213 showed that the Vpu region was responsible for the differing cytopathicity of these viruses. Although HIVMCK expressed Vpu protein, HIV213 did not because of a mutation at the start codon for Vpu. The amounts of envelope glycoprotein and virus particles associated with the cell surface were significantly increased on cells infected with Vpu-deficient viruses compared with Vpu-positive viruses. These data suggest that the highly cytopathic effects of HIV213 (Vpu-deficient) are due to an accumulation of envelope glycoprotein at the infected-cell surface, which would be caused by the retention of progeny virions in the absence of Vpu-facilitated virion release.

The nonstructural glycoprotein of rotavirus affects intracellular calcium levels

Rotavirus infection of monkey kidney cells has been reported to result in a significant increase in the concentration of intracellular calcium. This increase in intracellular calcium was associated with viral protein synthesis and cytopathic effects in infected cells. We tested the effect of individual rotavirus proteins on intracellular calcium concentrations in insect Spodoptera frugiperda (Sf9) cells. Insect cells were infected with wild-type baculovirus or baculovirus recombinants that contained an individual rotavirus gene. The cells were harvested at different times postinfection, and the intracellular calcium concentration was measured by using fura-2 as a fluorescent calcium indicator. We found that the concentration of intracellular calcium was increased nearly fivefold in infected Sf9 cells that expressed the nonstructural glycoprotein (NSP4) of group A rotavirus, and this increase in intracellular calcium concentration coincided with NSP4 expression. A similar result was observed in insect cells expressing NSP4 from a group B rotavirus, suggesting the conservation of this function among rotavirus groups. Expression of the other 10 rotavirus proteins or of wild-type baculovirus proteins in Sf9 cells did not significantly increase intracellular calcium levels. These results suggest that the nonstructural glycoprotein NSP4 is responsible for the increase in cytosolic calcium observed in rotavirus-infected cells.

Interactions between HIV-infected monocytes and the extracellular matrix: increased capacity of HIV-infected monocytes to adhere to and spread on extracellular matrix associated with changes in extent of virus replication and cytopathic effects in infected cells.

Monocytes express cell surface receptors for extracellular matrix (ECM) proteins of basement membranes. These receptors are engaged during extravasation of cells through capillary endothelium into tissue. The number of human immunodeficiency virus (HIV)-infected monocytes that adhered to ECM over 2 h was threefold higher than that of uninfected control cells. This difference was ECM specific and was not observed with a bovine serum albumin substrate. Enhanced adhesion to ECM was evident in monocytes by 4 days after HIV infection and increased through 10 days. Monocytes exposed to a T cell-tropic HIV strain that binds to but does not replicate in monocytes showed no changes in adherence to ECM. Thus, productive infection of monocytes by HIV induces a significant increase in the capacity of these cells to interact with ECM. Enhanced adhesion of HIV-infected monocytes to ECM was associated with increased spreading: at 12 h, sixfold more HIV-infected monocytes were spread on ECM than were uninfected control cells. Cell processes of HIV-infected monocytes formed a complex network on ECM: many of these cells expressed HIV proteins as detected by indirect immunofluorescence. HIV-associated cytopathic effects and levels of virion-associated reverse transcriptase activity depended on the substrate to which monocytes were attached. Virus replication and cytopathic effects in monocytes adhered to ECM, fibronectin, or plastic alone were comparable. In contrast, HIV-infected monocytes attached to laminin showed a significant increase in virus replication and in extent of cytopathic effects through 2 weeks after infection. The lowest levels of HIV replication and cytopathic effects were in monocytes attached to collagen IV. Interactions between monocytes and ECM profoundly affect the manner in which these cells control HIV infection: HIV infection changes the capacity of infected monocytes to attach and spread on ECM; attachment to ECM alters the extent of virus replication in infected cells.

Human Immunodeficiency Viruses and the Pathogenesis of AIDS

THE ACQUIRED immunodeficiency syndrome (AIDS) is caused by a newly recognized member of the lentivirus family, the human immunodeficiency virus (HIV). 1 This retrovirus family is distinct from the other subfamilies of human retroviruses, the Spumavirinae and Oncovirinae (Table 1). In particular, lentivirus genomes are large and contain several viral genes; the viruses frequently induce cytopathic effects in infected cells, and the disease they cause has a long incubation period resulting in immunologic disorders and neurological disease. 2 Lentiviruses have been identified in several other animal species, including horses, sheep, goats, cows, cats, and monkeys. 1,2 This finding suggests that a progenitor virus entered the animal kingdom in the distant past and various strains evolved over time within each species. This could be the reason that the primate and human lentiviruses (the simian immunodeficiency virus and HIV) resemble each other. 3 Two subtypes of HIV, HIV-1 and HIV-2, have been