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PubMed1990

Effect of antiviral antibody on maintenance of long-term rubella virus persistent infection in Vero cells.

A Vero cell line with a long-term rubella virus persistent infection was maintained for 45 weeks in the presence of anti-rubella virus antibody of sufficient titer to completely neutralize the virus in the culture fluid to determine the effect of the presence of antibody on the maintenance of the persistent infection. Prior to antibody treatment, virus was continuously detected as plaque-forming units in the persistently infected culture fluid. Virus clones that were plaque purified from the persistently infected culture fluid were temperature sensitive and exhibited a reduced efficiency of replication and ability to induce cytopathic effects in Vero cells at the persistently infected culture temperature compared with the standard virus used to initiate the persistently infected culture. Defective interfering RNAs were the major intracellular virus-specific RNA species present in the persistently infected cells. Treatment with antibody failed to cure the persistently infected culture of virus, and the cells retained the ability to release virus after antibody treatment was discontinued. Interestingly, the presence of antibody led to the selection of a population of virus which was markedly less cytopathic for Vero cells than the virus population which was selected during persistent infection in the absence of antibody.

Animals↗
PubMed1991

Characterization of the induction of persistence of major histocompatibility complex class II by hybrids of macrophages from bacillus Calmette Guerin-resistant mice.

Peritoneal macrophages (M phi) from mice that are resistant to infection by Mycobacterium bovis (strain BCG) (Bcgr) can be induced to express major histocompatibility complex (MHC) class II glycoproteins (I-A) continuously upon treatment with 100 units of recombinant interferon-gamma (rIFN-gamma). In contrast, M phi from mice that are susceptible to BCG (Bcgs) express I-A transiently. Persistent expression of I-A does not require the continued synthesis of the glycoprotein. Thus, treatment with cycloheximide (CHX) reduces I-A expression by M phi that express I-A transiently but does not affect the expression of I-A that is persistently expressed. It was not possible, in these studies, to characterize the induction of persistence independent of MHC class II expression because of the 24-48 h required for MHC class II synthesis and cycling to the cell surface. During this time, persistence was also induced. To characterize persistence independent of MHC class II induction we have produced M phi-M phi somatic cell hybrids that express I-A constitutively by fusing cells from a Bcgs M phi cell line with M phi from Bcgr mice. Treatment of some of the hybrids with CHX reduced MHC class II expression. The M phi hybrids required treatment with high doses of rIFN-gamma to induce CHX-resistant I-A expression. The induction of the persistence of I-A, following the addition of rIFN-gamma, required a short burst of protein synthesis as well as the presence of rIFN-gamma for at least 3 h. The addition of actinomycin D simultaneously with rIFN-gamma did not prevent the induction of the persistence of I-A expression by one of the M phi hybrids (F6.4). In contrast, the induction of persistence of I-A expression required a longer period of induction than was observed for hybrid F6.4, which was attributed to the requirement for new RNA and protein synthesis by the A1.8 hybridoma.

Animals↗
PubMed1988

The effects of carbon monoxide on persistent changes in young rat heart: cardiomegaly, tachycardia and altered DNA content.

Newborn rat pups that inhale 500 ppm carbon monoxide (CO) for 32 days and develop increased heart mass (i.e. cardiomegaly) show persistent cardiomegaly and elevated resting heart rate as adults. Studies were carried out to explore the relationship of these phenomena to CO concentration and initial cardiomegaly using exposures of 350, 500 and 700 ppm CO. Initial cardiomegaly was greater in the right ventricle free wall (RV) than in the left ventricle plus interventricular septum (LV + S) at all three CO concentrations, and RV mass excess increased with CO concentration. Initial RV cardiomegaly was greater at 350 and 700 ppm CO in females than in males. Persistent cardiomegaly in the RV also increased with CO concentration, and was significantly greater in the females. Persistent cardiomegaly in the RV increased with initial cardiomegaly but at a decreasing rate at the higher CO concentrations, and when expressed as a percentage of initial cardiomegaly (i.e. 'efficiency'), the relative response was greatest at 500 ppm CO. For LV + S, efficiency of development of persistent cardiomegaly was greatest at 350 ppm CO. Persistent tachycardia increased with CO concentration in males but failed to do so in females, and was only weakly correlated with degree of persistent cardiomegaly. Thus, persistent cardiomegaly and persistent tachycardia (in males) are related to CO concentration. Myocardial DNA content of 32-day-old juveniles was significantly increased at 350 and 700 ppm CO. Adult DNA content of the RV was significantly elevated at 350 ppm CO (females) and continued to rise with CO concentration. DNA concentrations of the RV and LV were increased at 700 ppm CO.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

M protein instability and lack of H protein processing associated with nonproductive persistent infection of HeLa cells by measles virus.

Persistent infections such as subacute sclerosing panencephalitis (SSPE) which do not produce infectious virus particles (nonproductive persistence) are often accompanied by a reduced steady-state amount of the viral matrix (M) protein and/or reduced hemadsorption activity. The possible causes of these aberrations associated with nonproductive persistence were investigated by following changes in the viral proteins with time in pulse-chase experiments. Three HeLa cell lines persistently infected with measles virus; K11, K11A, and HG111; were compared to each other and to acutely infected HeLa cells. K11 produces infectious virions at a low level (productive persistence). K11A and HG111 are both nonproductive persistently infected cell lines derived from K11. K11A cells have a reduced steady-state amount of viral M protein and reduced hemadsorption activity. HG111 cells have reduced hemadsorption but a normal level of viral M protein. As such, these cell lines serve as good model systems for the study of nonproductive persistent infection associated with SSPE. The reduced amount of M protein in K11A was found to result from rapid degradation of the protein. Degradation of the protein resulted from changes in the protein itself rather than from cellular changes. The hemagglutination (H) protein was found to be present at a low level in K11A cells. In addition, in both K11A and HG111 cells, conversion of the sugar moiety of the H glycoprotein from the high mannose form to the complex sugar form did not take place. Such modification usually occurs concomitant with transport of glycoproteins onto the cell surface. As such, lack of processing could preclude the appearance of functional H proteins on the cell surface. This could account for the reduced hemadsorption activity in these cells. The roles that these changes may play in the generation of nonproductive persistence are discussed.

Cell Transformation, Viral↗
PubMed1986

Persistent infection of Aedes albopictus C6/36 cells by Bunyamwera virus.

Two cell lines persistently infected with Bunyamwera virus have been established from the C6/36 clone of Aedes albopictus cells. The cells express Bunyamwera virus antigens as detected by immunofluorescence and are resistant to superinfection with Bunyamwera virus and other bunyaviruses, but not Dugbe virus (Nairovirus) nor vesicular stomatitis virus. The virus released from the persistently infected cells developed an altered cloudy or "bull's-eye" plaque morphology with increasing passage level, and a greater temperature sensitivity at 39.5 degrees than standard virus. The persistent virus interfered strongly with the replication of standard Bunyamwera virus in normal C6/36 cells and to a much lesser extent in BHK cells. Interference was not noted with other bunyaviruses or vesicular stomatitis virus. The persistent virus from one cell line, C6/36-PI LO, had a slower migrating nucleocapsid protein on polyacrylamide gels. Analysis of the RNA in persistently infected cells or in persistent virus by Northern blot hybridization with cloned cDNA probes showed that the major viral RNA species was the S segment, while the L and M RNA segments were barely detectable. Our results indicate that Bunyamwera virus can readily establish persistent infections in mosquito cells, and that persistence is accompanied by the generation of viruses with variable genetic and phenotypic characteristics.

Aedes↗
PubMed1986

Vero cells persistently infected with Tacaribe virus: role of interfering particles in the establishment of the infection.

Eight Vero cell sublines (Vero T) persistently infected with wild type Tacaribe virus replicated in different hosts were established. In order to unravel the mechanism involved in the initiation and maintenance of persistence, the properties of virus shed by the sublines and the presence of interfering particles (IP) were analyzed. During the course of infection, persistent virus (Tac-pi) underwent mutations although no consistent pattern of virus evolution was observed. ts mutants were isolated from two Vero T sublines, whereas a slow growth variant was shed by another. The remaining sublines released virus resembling wt parental virus. Except for Vero T1 sublines, Vero T cultures shed no detectable IP. These results emphasize the point that neither the emergence of virus mutants nor the synthesis of IP is essential for the maintenance of the persistent state. To define the role of IP in the initiation of persistence, coinfection experiments with a characterized inoculum were performed. For that purpose, attempts were made to obtain IP stocks free from pfu by serial transfers of undiluted virus. Neither enrichment nor amplification of IP occurred, and virus stocks were freed of infectious virus by UV irradiation. If normal Vero cells were infected with Tac-pi virus released by Vero T2, Vero T3, Vero T4, Vero T5, Vero T6, Vero T7 and Vero T10 sublines, a complete destruction of the monolayer without cell recovery was observed. In contrast, parental and Vero T1 viruses always originated persistently infected sublines. Similarly, the addition of IP to virus inocula constituted by Tac-pi viruses released by Vero T2, Vero T3, Vero T4, Vero T5, Vero T6, Vero T7 and Vero T10 sublines gave rise to persistently infected cultures. These results suggest that although IP are not important by themselves in the maintenance of persistence, they play a major role in initiation.

Animals↗
PubMed1986

Sensory registration and informational persistence.

The traditional view of iconic memory as a precategorical, high-capacity, quickly decaying visible memory has recently come under attack (e.g., Coltheart, 1980). Specifically, distinctions have been drawn between visible persistence, or the phenomenal trace of an extinguished stimulus, and informational persistence, knowledge about the visual properties of the stimulus. In the present research we tested two alternative conceptions of informational persistence. One conception is that visual information persists in a visual memory that begins at stimulus offset and lasts for 150-300 ms, independently of exposure duration. The second is that informational persistence arises from a nonvisual memory that contains spatial coordinates for displayed items along with identity codes for those items. Three experiments were conducted in which 3 X 3 letter arrays were presented for durations ranging from 50 to 500 ms. A single character mask presented at varying intervals after array offset cued report of an entire row of the array. Comparison of the cued row's masked and unmasked letters revealed that spatially-specific visual (i.e., maskable) information persisted after stimulus offset, regardless of exposure duration. This result favors the visual conception of informational persistence. But there was also support for the nonvisual conception: Accuracy increased and item intrusion errors decreased as stimulus duration increased. The implications of these results for models of informational persistence and for transsaccadic integration during reading are discussed.

Cues↗
PubMed1989

Persistent poliovirus infection of human neuroblastoma cells.

Two human neuroblastoma cell lines were persistently infected with poliovirus strains of all three serotypes. In persistently infected IMR-32 cells, which were studied in greatest detail, viral antigens were present in most cells, and over a 9-month period virions were found in the medium at high titers. Persistently infected cells were resistant to superinfection by Sabin 1, 2, and 3 poliovirus but sensitive to coxsackievirus B3. The viruses recovered from persistently infected cells were studied for conservation of epitopes, host cell specificity, and temperature resistance phenotype. The antigenic site 1 carried by the major capsid protein VP1 was modified on the persistent viruses of all three serotypes. This was confirmed for one virus by sequencing the corresponding genomic region in which two mutations were detected. The titers of persistent viruses were 1-3 log10 units higher on IMR-32 cells than on nonneuronal HEp-2 cells, while parental viruses had similar titers on both lines. When thermosensitive viruses were used to initiate the infection, the persistent viruses were found to be thermoresistant at 39 degrees C. Together the results indicate that the persistent infection correlated with the selection of highly mutated viral strains. Poliovirus-infected neuroblastoma cell lines thus constitute an in vitro model of chronic viral infections, which are increasingly implicated in human neural diseases.

Cell Line↗
PubMed1966

Persistence of nucleoli in short term and long term cell cultures and in direct bone marrow preparations in mammalian materials.

Persistent nucleoli were studied in Chinese hamster and human long term cultures, human peripheral blood short term cultures, as well as direct bone marrow preparations. No colchicine or hypotonic treatments were applied and the cells were differentially stained with the Feulgen method and light green. Nucleoli were found to persist in the three systems studied, although to a much greater extent in the long term culture. The persistent nucleolar materials were usually in the form of individualized nucleoli mainly at chromosome ends. They also sometimes existed in a fluidlike or dropletlike condition around the chromosomes. Association of acrocentrics in humans and end-to-end associations in hamsters are likely to result from persistence of nucleoli and the possible effects of colchicine and hypotonic treatments that are usually applied. Other phenomena, such as stickiness at metaphase and separation difficulties and fragmentation at anaphase, may result from persistence of nucleoli. Nucleoli were often associated with large chromosomes and sometimes at sites exhibiting faint or clear constrictions. The possibilities of a partial correspondence between sites of persistence and sites of organization, as well as of the organization of nucleolar materials at sites other than the main organizers, are discussed. The persistent nucleoli were not included in daughter nuclei. They either degenerated in the cytoplasm or were eliminated from the cell. The three systems used may represent different intensities of metabolism reflected in the amounts of nucleolar materials built up and the amount that persists.

Animals↗
PubMed1979

Persistence and pathogenicity of defective Friend spleen focus-forming virus. Decreased transplantability of hemopoietic cells as a marker for preleukemic change.

A latent form of persistent infection can be established in susceptible adult mice inoculated with a preparation of defective Friend spleen focus-forming virus (SFFV) purified free from standard leukemia-inducing helper virus (LLV-F). SFFV persistence was initially observed using an in vivo rescue technique in which SFFV could be directly rescued to form splenic foci of malignant erythropoiesis in mice. At approximately 30 d after virus inoculation however, SFFV could not be rescued after inoculation of LLV-F indicating that persistently infected (i.e., SFFV+) mice were either immume to exogenous helper virus or able to express SFFV-associated defective-interfering (DI) function(s). Persistent infection by SFFV was further documented using an in vitro rescue technique and ultimately resulted in the induction by SFFV of erythroleukemia in the absence of polycythemia or overt virus production. However, SFFV rescued by LLV-F from persistently infected normal and transformed hemopoietic cells was able to induce polycythemia in adult mice suggesting that this is a helper controlled property of the Friend virus complex. Transplantable SFFV-induced erythroleukemic cells could be retrieved from persistently infected yet histologically normal mice. The duration of SFFV persistence in normal spleen tissue suggests that the SFFV provirus resides in either a long-lived or pluripotent hemopoietic cell. Further, certain changes occurred, presumably in the membranes of persistently infected cells, which preceded the overt development of Friend leukemia and facilitated the definition of an SFFV preleukemic phase. Cell surface alterations were revealed using cell transfer techniques. Hemopoietic cells harboring a rescuable SFFV failed to proliferate when inoculated into lethally irradiated, syngeneic adult mice. In contrast, the transformed progeny of preleukemic cell populations and spleen cells transformed by FV complex (i.e., cells replicating both SFFV and LLV-F) were not rejected. This result suggests that histologically normal SFFV+ preleukemic cells express an antigen recognition site which is not present on overtly transformed cells and which may be a pertinent surveillance target for host anti-leukemogenic reactions.

Animals↗
PubMed1991

Influence of larval and adult nutrition on biting persistence in Aedes aegypti (Diptera: Culicidae).

Biting persistence was measured for Aedes aegypti (L.) mosquitoes given different levels of larval and adult nutrition. Persistence was measured as the total number of times during a 60-min trial that a mosquito returned to land on a defensive host after being disturbed and dislocated from the host, and as the rate of decline of landings over the 60 min test (pattern of persistence). Large females were significantly more persistent than smaller females, regardless of whether the females were provided water or 5% sucrose for 3 d before the test. Access to sucrose for 3 or 7 d did not influence the total number of landings of large females. Large females starved for 7 d exhibited significantly reduced persistence compared with large females starved for only 3 d. Water-fed specimens displayed a more rapid decline in the pattern of persistence than sucrose-fed specimens. Field-collected females, intermediate in size between the large and small laboratory females, had dry weights indicating they were relatively starved. They had a total number of landings similar to the small laboratory females and a persistence pattern similar to sucrose-fed specimens. Size-related differences in persistence may be one factor causing differences in parity rates and vector potential observed between large and small females in Ae. aegypti field populations.

Aedes↗
PubMed1991

Potential role of adherence traits of Escherichia coli in persistent diarrhea in an urban Brazilian slum.

We examined stools from 40 children with persistent diarrhea (duration, 14 days or more), from 50 children with acute diarrhea and from 38 control children to determine infectious etiologies for persistent diarrhea in Goncalves Dias, an urban favela (slum) in Fortaleza, Ceara, Brazil. Children with persistent diarrhea and children with acute diarrhea had similar rates of isolation of routine viral, bacterial and parasitic enteric pathogens. Routine pathogens were identified in at least 20% of cultures done more than 14 days into the diarrheal illness. We examined Escherichia coli isolated from these stools for adherence potential. Enteroaggregative E. coli were isolated significantly more often from children with persistent diarrhea than from control children or children with acute diarrhea (P less than 0.05). E. coli with hemagglutination patterns suggestive of adherence pili were also isolated more often from children with persistent diarrhea than from children with acute diarrhea (38% vs. 18%; P less than 0.05). Enterotoxigenic E. coli were isolated in combination with rotavirus more often from children with persistent diarrhea than from children with acute diarrhea. E. coli which were hydrophobic or exhibited hemagglutination were also seen more often in association with Giardia in children with persistent diarrhea. These findings suggest that the etiology of persistent diarrhea in children is complex and that the aggregative E. coli are associated with prolonged diarrheal illness. Although routine diarrheal pathogens may be present for more than 14 days, combinations of pathogens, including E. coli with adherence potential, may also contribute to prolonged diarrheal disease.

Animals↗
PubMed1988

Oligo-2',5'-adenylate synthetase activity in K562 cell lines persistently infected with measles or mumps virus.

Fluctuation of oligo-2',5'-adenylate synthetase (2-5AS) activity was examined in K562 cells infected with vaccine strains of measles virus (strains AIK-C and CAM-70) and mumps virus (strains Torii and Miyahara). Persistent infection was easily established in the mumps virus-infected cells without significant cytolysis or cell killing. In contrast, most of the cells infected with measles virus were killed by extensive cytolysis within 3 to 4 days. The small number of cells that did survive became persistently infected. That these persistently infected cells carried a virus antigen was confirmed by fluorescein isothiocyanate-labelled anti-measles virus rabbit antiserum and anti-mumps virus rabbit antiserum. The cells produced infectious progeny virus as well as interferon (IFN). Little induction of 2-5AS activity by IFN was demonstrated during the early stages of infection by these viruses. Similar results were observed in some of the persistently infected cells but not, however, K-CMP cells (K562 cells persistently infected with CAM-70) or K-MMP cells (K562 cells persistently infected with Miyahara). Failure to induce 2-5AS activity was unchanged in cells cultured for more than 6 months. The decrease of 2-5AS activity observed in K-MTP cells (K562 cells persistently infected with Torii) was the result of suppression of transcription of 2-5AS mRNA. On the other hand, a normal level of mRNA was found in K-AKP cells (K562 cells persistently infected with AIK-C). Therefore, it is suggested that the decrease of 2-5AS activity in K-AKP cells may be due to a failure to translate 2-5AS mRNA.

2',5'-Oligoadenylate Synthetase↗
PubMed1992

Association of indicators of hygiene behavior with persistent diarrhea of young children.

We examined the association between water and hygiene-related behaviors and persistent diarrhea (duration > or = 14 days) among children under age three years in an indigenous rural Guatemalan community. Behavior indicators were specific aspects of the appearance of the mother, study child, other children and household that could be observed using a spot observation technique. Thirty-four percent of children had one or more episodes of persistent diarrhea during the year of study. Bivariate analyses found that a higher proportion of observations in which the anti-hygienic condition was observed was significantly associated with persistent diarrhea for 11 of 26 behavior indicators; these 11 indicators were also strongly correlated with each other. In individual logistic regression models, which included overall rate of diarrhea and other child characteristics associated with persistent diarrhea, six behavior indicators maintained significant association with persistent diarrhea: presence of toy on the ground, presence of baby bottle on the ground, the hands of the mother being dirty, presence of a fecally soiled diaper on the ground in the household compound, presence of feces in the yard, and the study child wearing a fecally soiled diaper. Three additional indicators closely approached significant association with persistent diarrhea. Excluding the three soiled diaper indicators, which might be the result rather than the cause of diarrhea, we found the six other behavior indicators to demonstrate a significant dose-response effect in increasing risk of persistent diarrhea. These findings suggest that behaviors which promote increased exposure of young children to enteric pathogens increase risk of persistent diarrhea.

Behavior↗
PubMed1983

hipA, a newly recognized gene of Escherichia coli K-12 that affects frequency of persistence after inhibition of murein synthesis.

Except for a small fraction of persisters, 10(-6) to 10(-5), Escherichia coli K-12 is killed by prolonged inhibition of murein synthesis. The progeny of persisters are neither more resistant to inhibition of murein synthesis nor more likely to persist than normal cells. Mutants have been isolated in which a larger fraction, 10(-2), persists. The persistent response of the mutants, Hip (high persistence), is to inhibition of murein synthesis at early or late steps by antibiotics (phosphomycin, cycloserine, and ampicillin) or by metabolic block (starvation for diaminopimelic acid). Killing of the parent strain by each of the four inhibitors has two phases: The first is rapid and lasts about 30 min; the second is slower, but still substantial, and lasts 3 to 4 h. The first phase also occurs in the Hip mutants, but then viability of the mutants remains constant after about 30 min. Neither tolerance, resistance, impaired growth, nor reversion of spheroplasts accounts for high-frequency persistence. Two of the mutations map at 33.8 min in a region containing few other recognized functions. This position and the phenotypes define hipA as a newly recognized gene. Transposons Tn5 and Tn10 have been inserted close to hipA making it possible to explore the molecular genetics of persistence, a long recognized but poorly understood phenomenon.

Ampicillin↗
PubMed1984

Highly lytic and persistent lentiviruses naturally present in sheep with progressive pneumonia are genetically distinct.

Ovine and caprine lentiviruses share the capacity to induce slowly progressive and inflammatory diseases of the central nervous system (leukoencephalitis or visna), lungs (progressive pneumonia or maedi), and joints (arthritis) in their natural hosts. Studies on their replication indicated that ovine lentiviruses and caprine arthritis-encephalitis virus (CAEV) recently isolated in the United States establish persistent infection in ovine and caprine fibroblasts, whereas older prototype ovine lentiviruses such as Icelandic visna virus or American progressive pneumonia virus irreversibly lyse fibroblast cultures. Since all of the recent isolates were found to be persistent, Narayan et al. (J. Gen. Virol. 59:345-356, 1982) concluded that the highly lytic viruses were only tissue-culture-adapted strains. In the present report, we isolated new ovine lentiviruses from French sheep with naturally occurring progressive pneumonia which are either highly lytic (five isolates), as are the Icelandic strains of visna virus, or persistent (one isolate), as are CAEV or American persistent ovine lentiviruses. Protein and nucleic acid content analyses of these new highly lytic (type I) and persistent (type II) isolates indicated that type I and type II ovine lentiviruses were genetically distinct, type I and type II viruses being closely related to the Icelandic strains of visna virus and to CAEV, respectively. We conclude that (i) highly lytic ovine lentiviruses, such as the Icelandic prototype strains of visna virus and persistent lentiviruses more related to CAEV, are naturally present in the ovine species, and (ii) irreversible cell lysis induced by highly lytic viruses does not result from a tissue culture adaptation of field isolates that were originally persistent but is instead the consequence of a genetic content distinct from that of persistent viruses.

Animals↗
PubMed1986

Cell receptors for the mammalian reovirus: reovirus-specific T-cell hybridomas can become persistently infected and undergo autoimmune stimulation.

We have previously described the development of virus-specific helper T cell hybridomas which recognize structural determinants shared by type 1 and type 3 reoviruses that have been exposed to UV radiation. We have found that T-cell hybridomas become persistently infected with live type 3 reovirus used for the immunization. Persistently infected T-hybridoma cells were found to spontaneously produce interleukin 2 (IL-2). To analyze the mechanism of induction of IL-2 secretion of persistently infected T-cell hybridomas, we exposed T-cell hybridomas specific for UV-treated virus to replicating type 3 reovirus. The T-cell hybridomas became infected but did not produce IL-2 unless simultaneously exposed to syngeneic I-A+ antigen-presenting cells. In this situation, the persistently infected T-cell hybridomas produced IL-2 without being reexposed to virus. This process was not a consequence of nonspecific IL-2 gene activation, which occurs in cells persistently infected with reovirus, because reovirus infection did not activate IL-2 secretion in T-cell hybridomas with other antigenic specificities. Reovirus exposure also resulted in persistent infection of certain antigen-presenting B-cell tumor lines. The persistently infected B-cell tumor lines could stimulate reovirus-specific helper T cells but not T-cell hybridomas of other specificities. The data support the thesis that persistent infection of reovirus-specific T cells creates a mechanism in which the virus released from these cells is processed and then reexpressed by I-A+ antigen-presenting cells. The IA antigen and reovirus structures on the antigen-presenting cells then restimulate the T cells through their specific receptors, resulting in IL-2 synthesis and release. These observations may be relevant to mechanisms of autoimmunity induced by virus.

Animals↗
PubMed1990

Characterization of human parainfluenza virus type 3 persistent infection in cell culture.

Three cell lines persistently infected with human parainfluenza virus type 3 were characterized on a molecular level in this study. All six structural protein genes were transcribed into monocistronic RNAs in the persistently infected cells. In both acutely and persistently infected cells, polycistronic transcripts were abundant, although the ratio of polycistronic to monocistronic transcripts was reduced in the persistently infected cells. Each of the persistently infected cell lines contained a distinct subgenomic RNA species. The subgenomic RNAs were present in purified nucleocapsid cores, indicating that they represent viral genome RNA, were far more abundant than full-length RNA, and were stably maintained through at least 36 cell passages. Nucleotide sequence analysis of the subgenomic RNAs from two of the persistently infected cell lines revealed that the 5' ends are identical to that of the standard genome. Hybridization experiments with oligonucleotide probes showed that both fragments retain sequences from the 5' end of the standard genome and contain approximately 1,200 nucleotides (cell line 1) and 1,500 nucleotides (cell line 2) of the polymerase gene sequence. The demonstration of several alterations in viral gene expression in persistently infected cells offers insight into the factors associated with persistence of parainfluenza virus 3.

Animals↗