Clonal analysis of mammalian cell cultures persistently infected with Japanese encephalitis virus

More than 200 cells were cloned from populations of mammalian cells persistently infected with Japanese encephalitis virus. Only four cloned cultures contained cells that had viral antigen measurable by immunofluorescence and that released infectious virus, yet all clones harbored virus-specific RNA. Superinfection of cloned cells with wild-type Japanese encephalitis virus did not produce cytopathic effects, but resulted in production of viral antigen and infectious virus in formerly nonproducing clones. Cocultivation of nonproducer clone cells with normally permissive cells did not induce virus production, nor did treatment of nonproducer clones with various inhibitors of DNA, RNA, or protein synthesis. It is suggested that the cloning procedure may have selected for a particular subpopulation of cells and that defective virus is also involved in establishment and maintenance of persistent infection.

Japanese encephalitis virus in mosquito salivary glands

Culex tritaeniorhynchus and C. pipiens mosquitoes were infected with Japanese encephalitis virus either by intrathoracic injection or by membrane feeding. The virus maturation sites and the process of virus particle concentration in salivary gland cells were studied by electron microscopy. Occurrence of mature virions was primarily associated with intracytoplasmic viral matrices which were extraordinarily large and had a perinuclear location in C. pipiens mosquitoes. The other sign of virus replication was the proliferation of small spherical vesicles throughout the cytoplasm. It appeared that mature virions were entrapped in intracellular vacuoles and later released into the apical cavity of salivary gland cells through the fusion of these vacuoles with the apical plasma membrane. This process seemed to be associated with primary resynthesis of saliva in mosquitoes following blood feeding activity. Another type of shedding involved virus particles either singly or in mass being released directly through the apical plasma membrane. All of these events occurred only in cells of the lateral lobes of the salivary glands, which fact was confirmed by immunofluorescent staining of infected glands. The median lobe of mosquito salivary glands may have a minor or no role in the transmission of Japanese encephalitis virus.

Neutralization tests for dengue and Japanese encephalitis viruses by the focus reduction method using peroxidase-anti-peroxidase staining

Neutralization tests were made on 4 types of dengue (DEN) virus and Japanese encephalitis (JE) virus by incubation of serially diluted antisera and constant amounts of the viruses and then focus assay of surviving virus infectivity with peroxidase-anti-peroxidase (PAP) staining. Neutralization reactions were virtually completed in 2 hr on incubation of serum-virus mixtures at 28 C. A straight regression line was obtained on a probit chart by plotting the focus reduction rates at various dilutions of a given serum against the logarithm of the serum dilution used in the test. The slopes of the probit regression lines for the neutralization for DEN types 1 and 3 were similar, but differed somewhat from those for DEN type 2 and type 4. The slope of the line for JE virus was quite different from those for DEN viruses. Using these relations, the fifty percent focus reduction titer (FR50) of neutralizing antibodies of a given serum could be estimated from the focus reduction rates at several dilutions of the test serum when the latter was between 25-75% of the value of the control.

Effects of protamine sulfate on dengue type 1 viral activities

Protamine treatment of type 1 dengue-infected mouse brain suspension resulted in precipitation of several viral specific activities. Complement-fixation activity was almost completely precipitated by protamine. The complement-fixation components recovered in the precipitate were comparable to a non-precipitated reference dengue 1 antigen in their homologous and heterologous reactions. Dengue hemagglutinin was also precipitated by the same treatment. The precipitated hemagglutinin was resolved into three components by buoyant density centrifugation, whose densities were 1.236, 1.215, and 1.178 g/ml, respectively. Three similar HA components were detected in non-protamine treated virus preparations. In both instances the highest-titered HA fraction possessed a buoyant density of 1.21--1.22 g/ml. These HA components were tested in the hemagglutination-inhibition reaction and were proved to be virus-specific. Cesium chloride density gradient centrifugation was shown to be useful for removing possible inhibitor(s) of viral specific hemagglutinin.

Transovarial transmission of Japanese encephalitis virus by mosquitoes

Female Aedes albopictus and Aedes togoi mosquitoes infected with Japanese encephalitis virus either by intrathoracic inoculation or by ingestion of a virus-sucrose-erythrocyte mixture transmitted the virus to a small percentage of their F1 progeny. Adult F1 female Aedes albopictus thus infected transmitted the virus in turn to newly hatched chickens by feeding on them.

Persistent infection of cultured mammalian cells by Japanese encephalitis virus

Persistent infections were established by serial undiluted passage of flavivirus Japanese encephalitis virus in a line of rabbit kidney cells (MA-111). The persistently infected cells resembled uninfected cells in most respects. Low levels of infectious virions were released from a small percentage of cells, and a larger and more variable percentage was shown to possess viral antigen by fluorescent-antibody staining. Released viruses were shown to interfere with replication of wild-type Japanese encephalitis virus. Persistently infected MA-111 cells could not be superinfected with homologous wild-type Japanese encephalitis virus but could be superinfected with two heterologous viruses. Transfer of cell culture medium from persistently infected MA-111 cells to a line of African green monkey kidney cells (Vero) resulted in similar persistent infections in the latter cells. Temperature sensitivity and host-cell interferon production were not involved in establishment or maintenance of persistence. Determination of ratios of physical particles to infectious particles revealed that many defective, noninfectious viruses were present, suggesting that defective interfering particles may be responsible for persistency.

A spontaneous temperature sensitive mutant of Japanese encephalitis virus: preliminary characterization

A spontaneously arising temperature sensitive (ts) mutant of Japanese encephalitis virus (JEV), ts104, was isolated from chick fibroblast (CF) cell cultures of JEV strain M 1/311. Strain ts104 was plaque purified and characterized to ascertain its potential as a candidate for a live vaccine. Parameters of its growth, temperature lability, immunogenicity and virulence were examined. Ts104 has been shown to be stable ts JEV strain, multiplying as well as the parent strain in CF cultures at 35 degrees C, but not mutiplying at 39 degrees C. It was avirulent for embryonated chicken eggs incubated at 39 degrees C and of reduced virulence for intracerebrally (i.c.) inoculated mice as measured by LD50 in weanling mice and average day of death in weanling and suckling mice. Intraperitoneal injection of adult mice with either parent or ts strain resulted in similar levels of protection against challenge with either strain. The potential of ts104 as a candidate live JEV vaccine strain is discussed.

Plaque formation by alphavirus (Getah) in Culex Mosquito cells

Plaques were formed by Getah virus (an Alphavirus) which had been grown in BHK cells and passaged once in Culex cells before inoculation of Culex cell cultures. Plaques were not produced either by Getah or Japanese encephalitis (JE) viruses which had been passaged only in BHK cells. Plaque counts in Culex cell monolayers were almost the same as in BHK cells.

Interspecies interactions of arboviruses. II. Participation of the genomes of two flaviviruses, West Nile and Japanese encephalitis, in formation of a virus clone with dual antigenic determinants

A peculiar clone, 41/WN+JE+, possessing antigenic determinants of a flaviviruses, West Nile (WN) and Japanese encphalitis (JE), is described. The antigenic duality of this clone exceeded the cross reactions between WN and JE viruses; either antiserum neutralized 104--105 PFU/ml of the virus. The property of antigenic duality was inherited in over 340 virus generations and retained upon propagation in selective cell systems and after recloning. The progeny of infectious RNA consisted of 3 types of virus particle: antigenetically distinct WN and JE viruses and particles retaining dual antigenic determinants WN+JE+. The nature of clone 41/WN+JE+ (a stable heterozygote accompanied by phenotypic mixing) and its origin due to inadvertent contamination of attenuated WN virus with JE virus is discussed.

Biological and immunological studies on two substrains, c-1 and c-3, derived from the Nakayama-NIH strain of Japanese encephalitis virus

A comparative analysis was performed on two substrains, c-1 and c-3, derived from the Nakayama-NIH strain of Japanese encephalitis virus. The infectivity of the two substrains was inactivated at similar rates by treatment with Tween 80 and Tween 20 but not by treatment with Tween 60. However, hemagglutinating activity as measured at pH 6.8 of the c-3 substrain treated with Tween 80 was more labile than that of the c-1 substrain treated with Tween 80. Also, the immunogenicity (neutralizing and hemagglutination-inhibiting antibodies) was different between the two substrains in sensitivity to low pH (6.8) and to Tween 80. With the c-1 substrain a combination of these treatments reduced the immunogenicity, but each treatment applied singly did not materially reduce it. The immunogenicity of the c-3 substrain was reduced by single as well as combined applications of the two treatments. Evidence was obtained which suggested that the part of the antigen sensitive to these treatments was strain-specific, whereas the resistant antigen was common among the Japanese encephalitis-St. Louis encephalitis complex members.

Interspecies interactions of arboviruses. I. Competition phenomenon in mixed populations of Japanese encephalitis and West Nile viruses

Two phenomena, competition and independent reproduction, were observed on co-cultivation of Japanese encephalitis (JE) and West Nile (WN) viruses in permissive systems. Competition occurred in populations propagated in mouse brains and led to elimination of JE virus. Only clones of WN virus were isolated from these populations at the 1st-3rd passage level. No competition was observed in mixed infection of primary Syrian hamster kidney (SHK) cell culturess the population had the combined immunological phenotype JE+WN+, and contained discrete JE and WN virus clones and clones with duplex antigenic markers. Upon subcloning, the latter dissociated into JE and WN viruses. The competition phenomenon depended upon 3 factors: co-cultivation system, peculiarities of the virus strains, and virus dose. The capacity of WN virus strains to eliminate JE virus in mixed infection of mice varied.

Natural and experimental infections of Japanese tree sparrows with Japanese encephalitis virus

20 to 37 per cent of wild Japanese tree sparrows had neutralizing antibodies to Japanese encephalitis virus (JEV). Sparrows free of antibodies were inoculated with 10,000 plaque-forming units of JEV. None of the birds became clinically ill. Virus could be detected in blood plasma during the first 3 days after inoculation but not thereafter. Neutralizing antibodies started to appear at 4 days after inoculation and the response was of variable duration, in some cases extending up to 200 days after inoculation.

The effect of octadecenoic acid on the growth of japanese encephalitis virus in Novikoff hepatoma cells

The growth characteristics of Japanese encephalitis virus cultivated in Novikoff hepatoma cells grown in shaker culture can be differentially altered by the presence of 6-cis or cis-9-octadecenoic acid in Swim's 67-G medium. The addition of 125 mug of the 6-isomer per ml medium reduced the number of infectious particles produced, whereas the same amount of the 9-isomer enhanced virus production. The virus was found to be more stable in cell-free spent medium than in fresh medium. The presence of 125 mug 6-18:1 per ml in fresh medium resulted in a rapid loss of virus infectivity.

Studies on neutralization of Japanese encephalitis virus. IV. Effect of anti-cellular serum on the neutralization of sensitized virus by anti-rabbit IgG serum

The effect of anti-cellular rabbit serum (ACRS) on the neutralization of sensitized Japanese encephalitis virus (JEV) by anti-rabbit IgG serum was examined to elucidate the interaction between virus-antibody complex and the surface of the host cells during the process of neutralization. ACRS had no effect on the adsorption of either sensitized or non-sensitized virus, but was able to restore the lost infectivity of sensitized virus which occurred during the process of neutralization by anti-rabbit IgG serum. This restoration of infectivity was found to take place not only by the addition of ACRS to the reaction mixtures (virus-antibody, anti-rabbit IgG complex) but also by pretreatment of the host cells with ACRS. Although the restoration of lost infectivity varied in magnitude with the concentration of ACRS used, it never exceeded the infectivity titer of the sensitized virus befor incubatio with anti-rabbit IgG serum. This result suggests that ACRS has no ability to reverse the neutralization by anti-viral serum. Since the ACRS reacted only with anti-rabbit IgG serum treated sensitized virus, resulting in an increase of the number of infectious centers, the restoration of lost infectivity was explained as being due to the enhancement of adsorption of sensitized virus to the host cells by bridge formation of anti-rabbit IgG antibody between them.

Viral polypeptide composition of Japanese encephalitis virus-infected cell membranes

Chick embryo cells infected with Japanese encephalitis virus were separated into smooth and rough membrane fractions, as judged by electron microscopy. Polyacrylamide gel electrophoretic analysis of the membrane fractions showed them to contain all of the virus specific polypeptides; however, the relative proportions of the polypeptides varied among smooth and rough membranes. The relationship of these observations to current concepts of group B arbovirus morphogenesis is discussed.

[Study of organ cultures of human embryonic intestines infected with the human cytomegalovirus and the Japanese encephalitis virus]

Reproduction of human cytomegalovirus (CMV) and Japanese encephalitis virus (JE) was studied in organ cultures of human embryo intestine under conditions of mono- and combined infection. The titer of JE virus in monoinfection reached its maximum level (10(7) TCD50/ml) whereas the titer of CMV did not exceed 10(2) TCD50/ml. In combined infection the titer of CMV increased to 10(5.5) TCD50/ml and the titer of JE virus remained at the same level (10(7) TCD50/ml). The results obtained in light and scanning electron microscopy studies indicate that in monoinfection CMV causes considerably earlier and more profound degenerative changes in mesanchymal elements of embryonal intestinal tissues than does JE virus. At the same time the combined infection of organ cultures with these viruses is not cytocidal.

Use of duck embryo cell cultures for the study of arbovirus reproduction

Duck embryo cell (DEC) cultures were used for the study of arbovirus reproduction. High sensitivity of DEC cultures to Japanese encephalitis, West Nile, Tyuleniy, Sakhalin and Baku viruses was established. DEC cultures are recommended for investigation of arbovirus reproduction.

Growth of Japanese encephalitis virus in Culex tritaeniorhynchus cell cultures

Ovarian cells from the mosquito Culex tritaeniorhynchus established in continuous tissue cultures have been found to support the growth of Japanese encephalitis virus with titers reaching as high as 10(7.36) MICLD50 per 0.03 ml. Virus-cell cultures were serially subcultured 60 times over 300 days and the virulence of the virus was determined after each passage. A gradual loss in virus titer was observed, with titers always higher in the medium than in the cells. Cytopathogenic effects were not observed in the infected cell cultures, either in primary or subsequent passages. However, the cell growth rate suggested that the cells may have been metabolically or mechanically damaged. The chromosome complement of the cells remained unchanged. Direct-fluorescent antibody studies during early and late passages revealed a loss in virus infectivity from chronically infected cells which may have been due to a gradual decrease in virus replication as the passages increased. The infectivity of virus particles, however, returned to previous levels after passage into fresh cell cultures. The loss of virus particles during serial passage may be correlated with the condition of the cells.

Adaptation of BHK-21 cells to growth in shaker culture and subsequent challenge by Japanese encephalitis virus

Baby hamster kidney (BHK-21) cells were adapted to grow in shaker culture using Waymouth medium 752/1 containing 20 mM N-2-hydroxyethyl-piperazine-N'-2'-ethanesulfonic acid buffer and supplemented with 2.5% (vol/vol) calf serum, 0.002% (wt/vol) sodium oleate, and 0.2% fatty acid-free bovine serum albumin (WO2.5). Infectivity of Japanese encephalitis virus grown in the cells adapted to WO2.5 approached 2 x 10(8) plaque-forming units per ml. The culture volume of infected cells was reduced fivefold 12 h after infection. This step resulted in a 10-fold increase in infectivity over that obtained from infected cultures not subjected to volume reduction.