Dengue carrier culture and antigen production in human lymphoblastoid lines

Replication of dengue type 2 (D2) viruses was studied in four lymphoblastoid cell lines; Raji, HR1, EB3 and RPMI 6410. The HR1 cell line failed to support D2 growth while the other cell lines showed varying susceptibility. Both D2 strain 16681 and strain New Guinea C (NGC) passaged in LLC-MK2 cells replicated readily in Raji cells, while a high mouse-brain-passaged NGC strain did not. A soluble complement-fixing (SCF) antigen from D2-infected Raji cells showed lines of identity with a D2SCF antigen prepared from infected suckling mouse brains. Electron microscopic studies of a D2 Raji carrier culture showed that virions were located in a membrane-vesicle complex in the cytoplasm of the cells. Precursors of viral particles were more frequently observed in the parts of the vesicle which had rough endoplasmic reticular membranes. Mature virus particles were observed often at the boundary of the other part of the vesicle, which consisted of smooth endoplasmic reticulum. Occasionally, a large crystalloid structure consisting of incomplete viral particles was seen in degenerative cells. Dengue carrier cultures in human lymphoblastoid lines may provide a convenient in vitro system for study of aspects of dengue virus-leukocyte interactions.

Vector capability of Aedes aegypti mosquitoes for California encephalitis and dengue viruses at various temperatures

A Yukon strain of California encephalitis virus (snowshoe hare subtype) was transmitted by bites of laboratory-bred Aedes aegypti mosquitoes after 3 weeks of extrinsic incubation at 80°F and after 4 weeks at 55°F after intrathoracic injection. Transmission first occurred after 4 weeks incubation at 80 or 55°F when mosquitoes were infected by feeding. Zero-passage strains of dengue-2 virus were transmitted after 6 days of extrinsic incubation at 90°F after feeding or intrathoracic injection, after 6 to 13 days incubation at 75°F following injection, after 13 days at 80°F following feeding, and after 13 to 27 days at 55°F following injection. Although virtually all mosquitoes were infected at the time transmission occurred, California encephalitis virus was transmitted by less than 50% of mosquitoes, but 80% or more of mosquitoes infected with the dengue-2 strains transmitted virus. Enveloped virions about 35 nm diameter were observed in the cytoplasm of acini of salivary glands of mosquitoes infected with dengue-2 virus.

Dengue virus infection of mice: morphology and morphogenesis of dengue type-2 virus in suckling mouse neurones

In dengue type-2 virus-infected neurones of suckling mice, formation of single-membrane vesicles is observed in the distended cisternae of the endoplasmic reticulum mostly of the perinuclear zone around 72 h after inoculation. Electron-dense 50-nm virus particles are arranged in chains in these distended cisternae; some form small crystalloid aggregates. Aberrant particles of different shapes are also seen in the distended cisternae about the same time that the virus particles appear. Parallel filamentous structures are occasionally observed in the cisternae that contain very few virions, either characteristic or aberrant. Increasing cytopathic changes are present after 75 to 96 h. There is an intense vesicular formation. Large numbers of virions and aberrant particles are seen either in the endoplasmic reticulum cisternae or smooth membrane vesicles. They are spread throughout the neurocytoplasm, extending into the dendrites. Dengue virions which are enclosed in fairly intact membrane-bound vesicles are released during cytolysis of the neurones. Morphogenesis of dengue virus type 2 is discussed.

Replication of dengue virus type 2 in Aedes albopictus cell culture

The replication of type 2 dengue (D-2) virus in Aedes albopictus (Aal) mosquito cell cultures differed from that in vertebrate (LLC-MK2) rhesus monkey kidney cells. Virus readily replicated in Aal cells at either 30 or 37 C, but had no apparent effect on the host cell. Persistent infection was established with continual virus production for at least 6 months, although the virulence of progeny virus for both suckling mice and LLC-MK2 cells became attenuated. Density gradient analysis of infected Aal cell supernatant products indicated that only complete virus was released, in contrast to infected LLC-MK2 cells which also released incomplete virus. The surface antigens of the virus produced in Aal cells appeared to be considerably modified in that antiserum to vertebrate cell-produced D-2 virus did not block hemagglutination, whereas anti-Aal cell antiserum did. Virus infectivity could be neutralized by the antiserum to D-2 virus grown in vertebrate cells, however. Virus produced in LLC-MK2 cells did not demonstrate a similar host-cell modification. These results may reflect a difference in the mechanism by which D-2 virus matures in Aal cells.

Immunological and biophysical separation of dengue-2 antigens

Antigenic compositions of slowly sedimenting dengue-2 hemagglutinin (SHA) and soluble complement-fixing antigen (SCF) were compared with the virion (rapidly sedimenting hemagglutinin, RHA) by radioimmune precipitation (RIP), RIP inhibition, kinetic neutralization, and neutralization blocking tests with the use of hyperimmune mouse ascitic fluids. RHA and SHA were unable to inhibit completely the RIP of each other by anti-RHA, and neutralization by anti-RHA was not blocked by SHA. This indicated that SHA is serologically related, but not identical, to RHA. SHA differed from RHA in that SHA lacked the "core" polypeptide but contained the two envelope polypeptides. In addition, SHA contained a polypeptide with a molecular weight of 16,500 daltons and a suggestion of several other proteins. These data, when considered with other evidence, suggest that SHA is a special form of "incomplete virus." SCF was unable to inhibit the RIP of SHA or RHA or to block neutralizing antibodies. Further, anti-SCF did not neutralize RHA or precipitate significant levels of SHA or RHA. Polyacrylamide gel electrophoresis separated SCF from structural polypeptides by molecular size. This evidence suggests that SCF is a nonstructural antigen.

Dengue virus plaque development in simian cell systems. I. Factors influencing virus adsorption and variables in the agar overlay medium

Chemical and physical variables influencing the plaquing of all dengue serotypes in two simian cell systems were studied. Calf serum in the nutrient overlay may be replaced by mouse ascitic fluid or bovine plasma albumin when employing the rhesus monkey kidney LLC-MK(2) cell system for plaquing all dengue serotypes. Doubling the serum concentration in the overlay had little effect in modifying dengue types 1, 2, 3, and 4 plaque titers. Newborn agamma, 4-week-old and 8-week-old calf serum gave comparable titers with all dengue virus serotypes. Dengue virus titers, plaque size, and development time were unaffected by sodium bicarbonate concentrations ranging from 1.1 to 4.4 mg/ml of overlay. A twofold increase (0.00332 g%) in the amount of either autoclaved or filtered-sterilized neutral red reduced the dengue 2 virus titer as much as 2.2 logs. An increased Mg(++) and decreased Ca(++) concentration in the overlay medium increased the efficiency of the plaquing system.

Dengue virus plaque development in simian cell systems. II. Agar variables and effect of chemical additives

Dengue type 2 virus, strain New Guinea B, plaqued with equal facility and titer under overlays containing six different grades of commercial agar in the LLC-MK(2) cell system. Doubling the agar volume on LLC-MK(2) cell monolayers increased the plaque development time of dengue type 1, strain Hawaii. Storage of agar at 56 C reduced or totally abolished dengue type 4, strain H-241, plaque titer in LLC-MK(2) cells. The influence of six known virus plaque-enhancing compounds on plaque development of all dengue virus serotypes was studied in two continuous simian kidney cell lines, LLC-MK(2) and Vero. In the absence of any chemical additive, plaque development of all dengue serotypes was more rapid (4 to 10 days) in the LLC-MK(2) line than in the Vero line (6 to 13 days). Increased plaque development time of type 1, strain Hawaii, by pancreatin and plaque-size doubling of dengue types 1 and 4 was the only advantage conferred by the addition of six chemical additives in the LLC-MK(2) cell system. Dengue types 1 and 6 failed to plaque in the Vero cell system unless aided by a plaque-enhancing compound; plaques of dengue types 2, 3, 4, and 5 appeared sooner (2 days) and were increased in plaque diameter. The optimal DEAE concentration for plaquing dengue type 1, strain Hawaii, was 100 mug/ml; plaque development either failed at lower concentrations or was inhibited at higher (200 mug/ml) concentrations.