Chimeric tick-borne encephalitis and dengue type 4 viruses: effects of mutations on neurovirulence in mice

Two new chimeric flaviviruses were constructed from full-length cDNAs that contained tick-borne encephalitis virus (TBEV) CME or ME structural protein genes and the remaining genes derived from dengue type 4 virus (DEN4). Studies involving mice inoculated intracerebrally with the ME chimeric virus indicated that it retained the neurovirulence of its TBEV parent from which its pre-M and E genes were derived. However, unlike parental TBEV, the chimeric virus did not produce encephalitis when mice were inoculated peripherally, indicating a loss of neuroinvasiveness. In the present study, the ME chimeric virus (vME) was subjected to mutational analysis in an attempt to reduce or ablate neurovirulence measured by direct inoculation of virus into the brain. We identified three distinct mutations that were each associated independently with a significant reduction of mouse neurovirulence of vME. These mutations ablated (i) the TBEV pre-M cleavage site, (ii) the TBEV E glycosylation site, or (iii) the first DEN4 NS1 glycosylation site. In contrast, ablation of the second DEN4 NS1 glycosylation site or the TBE pre-M glycosylation site or amino acid substitution at two positions in the TBEV E protein increased neurovirulence. The only conserved feature of the three attenuated mutants was restriction of virus yield in both simian and mosquito cells. Following parenteral inoculation, these attenuated mutants induced complete resistance in mice to fatal encephalitis caused by the highly neurovirulent vME.

Dengue virus protein recognition by virus-specific murine CD8+ cytotoxic T lymphocytes

The identification of the protein targets for dengue virus-specific T lymphocytes may be useful for planning the development of subunit vaccines against dengue. We studied the recognition by murine dengue virus-specific major histocompatibility complex class I-restricted, CD8+ cytotoxic T lymphocytes (CTL) of dengue virus proteins using recombinant vaccinia viruses containing segments of the dengue virus genome. CTL from H-2k mice recognized a single serotype-cross-reactive epitope on the nonstructural (NS) protein NS3. CTL from H-2b mice recognized a serotype-cross-reactive epitope that was localized to NS4a or NS4b. CTL from H-2d mice recognized at least three epitopes: a serotype-specific epitope on one of the structural proteins, a serotype-cross-reactive epitope on NS3, and a serotype-cross-reactive epitope on NS1 or NS2a. Our findings demonstrate the limited recognition of dengue virus proteins by CTL from three inbred mouse strains and the predominance of CTL epitopes on dengue virus nonstructural proteins, particularly NS3. Since human dengue virus-specific CTL show similar patterns of recognition, these findings suggest that nonstructural proteins should be considered in designing vaccines against dengue.

Construction and characterization of chimeric tick-borne encephalitis/dengue type 4 viruses

Dengue type 4 virus (DEN4) cDNA was used as a vector to express genes of the distantly related tick-borne encephalitis virus (TBEV). Full-length chimeric TBEV/DEN4 cDNAs were constructed by substituting TBEV genes coding for proteins such as capsid (C); pre-membrane, which is the precursor of membrane (M); envelope (E); or nonstructural protein NS1 for the corresponding DEN4 sequences. RNA transcripts prepared from cDNAs were used to transfect permissive simian cells. Two viable chimeric viruses that contained TBEV CME or ME genes were recovered. Compared with DEN4, chimeric TBE(ME)/DEN4 virus [designated vTBE(ME)/DEN4] produced larger plaques and grew to higher titer in simian cells. In contrast, vTBE(ME)/DEN4 produced smaller plaques on mosquito cells and grew to lower titer than DEN4. Analysis of viral RNA and proteins produced in vTBE(ME)/DEN4- and DEN4-infected mosquito or simian cells revealed that the chimera was restricted in its ability to enter and replicate in mosquito cells. In contrast, vTBE(ME)/DEN4 entered simian cells efficiently and its RNA was replicated more rapidly in these cells than was parental DEN4 RNA. Following intracerebral inoculation, vTBE(ME)/DEN4 caused fatal encephalitis in both suckling and adult mice, while nearly all mice inoculated by the same route with DEN4 did not develop disease. Unlike wild-type TBEV, vTBE(ME)/DEN4 did not cause encephalitis when adult mice were inoculated by a peripheral route. Adult mice previously inoculated with the chimera by a peripheral route were completely resistant to subsequent intraperitoneal challenge with 10(3) times the median lethal dose of TBEV, whereas mice previously inoculated with DEN4 were not protected. These findings indicate that (i) the TBEV M and E genes of the chimeric virus are major protective antigens and induce resistance to lethal TBEV challenge and (ii) other regions of the TBEV genome are essential for the ability of this virus to spread from a peripheral site to the brain. Success in constructing a viable TBEV/DEN4 chimera that retains the protective antigens of TBEV but lacks its peripheral invasiveness provides a strategy for the development of live attenuated TBEV vaccines.

Construction of intertypic chimeric dengue viruses by substitution of structural protein genes

Dengue virus contains an 11-kilobase positive-strand RNA genome that codes for, in one open reading frame, three structural proteins (capsid, premembrane, and envelope), followed by seven nonstructural proteins. The structural protein genes of a full-length cDNA clone of type 4 dengue virus were replaced with the corresponding genes of dengue 1 or dengue 2 to create intertypic chimeric cDNA. The RNA transcripts made from these templates were infectious when transfected into permissive cells in culture. Progeny of chimeric cDNA produced apparently authentic dengue 1 or dengue 2 structural proteins, together with dengue 4 nonstructural proteins, and as a consequence exhibited type 1 or type 2 serological specificity. Both of the chimeras ultimately grew to the same titer as their type 1 or type 2 parent, but the type 2/type 4 chimera grew very slowly. This chimera also produced small plaques; in contrast, the type 1/type 4 chimera produced normal size plaques. The type 2/type 4 chimera retained the mouse neurovirulence of the dengue 2 virus, which was the source of its structural protein genes. Each of the mice inoculated intracerebrally with the chimera died, but survival time was prolonged. The retardation of replication of the type 2/type 4 chimeric virus suggests that this virus and possibly other intertypic dengue virus chimeras with similar properties should be examined for attenuation in primates and possible usefulness in a live dengue virus vaccine for humans.

Dengue virus premembrane and membrane proteins elicit a protective immune response

We have constructed recombinant vaccinia viruses that express the premembrane (pre-M), membrane (M), or the cleaved, residual portion of pre-M (non-M) proteins of dengue 4 virus, or the pre-M, non-M, or envelope (E) proteins of dengue 2 virus, to evaluate their ability to induce protective immunity in mice. Cells infected with these recombinants make proteins of expected size. Mice immunized with recombinants expressing dengue 4 pre-M or M were protected against subsequent dengue 4 encephalitis challenge, but non-M was not protective. However, a recombinant that expressed both pre-M and E as a polyprotein gave solid protection, while the simultaneous administration of the two recombinants expressing pre-M and E gave a significant level of protection. Pre-M and M function as antigens eliciting a protective immune response, and the combination of pre-M plus E is more protective than E alone.

Infectious RNA transcribed from stably cloned full-length cDNA of dengue type 4 virus

Dengue virus is an enveloped positive-strand RNA virus with a genome approximately 11 kilobases in length. The four serotypes of dengue virus are currently the most important members of the flavivirus family in terms of geographical distribution and the incidence of infection in humans. In this communication we describe successful cloning of a stable full-length cDNA copy of dengue type 4 virus that can be used as the template for in vitro transcription of infectious RNA. Evidence is presented that dengue virus recovered from permissive cells transfected with the in vitro RNA transcripts retained a mutation that was engineered into full-length cDNA. The properties of the virus produced by cells transfected with infectious RNA transcripts of dengue cDNA resembled those of the virus from which the cDNA clone was derived. The dengue virus recombinant DNA system should prove helpful in gaining a better understanding of the molecular biology of dengue viruses and should facilitate the development of a safe and effective live vaccine for use in humans.

Immunization of mice with recombinant vaccinia virus expressing authentic dengue virus nonstructural protein NS1 protects against lethal dengue virus encephalitis

The protective immunity conferred by a set of recombinant vaccinia viruses containing the entire coding sequence of dengue virus type 4 nonstructural glycoprotein NS1 plus various flanking sequences was evaluated by using a mouse encephalitis model. Mice immunized with recombinant vNS1-NS2a, which expresses authentic NS1, were solidly protected against intracerebral dengue virus challenge. However, mice immunized with recombinants vNS1-15%NS2a and vRSVG/NS1-15%NS2a, which express aberrant forms of NS1, were only partially protected (63 to 67% survival rate). Serologic analysis showed that mice immunized with vNS1-NS2a developed high titers of antibodies to NS1 as measured by radioimmunoprecipitation, enzyme-linked immunosorbent assay, and complement-mediated cytolytic assays. In addition, a pool of sera from these animals was protective in a passive transfer experiment. Lower titers of NS1-specific antibodies were detected in sera of animals immunized with vNS1-15%NS2a or vRSVG/NS1-15%NS2a by all three assays. These data support the view that protection against dengue virus infection in mice may be mediated at least in part by NS1-specific antibodies through a mechanism of complement-mediated lysis of infected cells. Additionally, immunization with two recombinant viruses expressing authentic NS1 of dengue virus type 2 conferred partial protection (30-50%) against dengue virus type 2 challenge.

Direct and indirect contractile responses of the human vas deferens and actions of noradrenaline and of calcium antagonists

Contractile responses of the isolated human vas deferens, obtained from vasectomy operations, were measured. Large single electrical shocks gave a twitch response with short latency (0.36 s) which was insensitive to prazosin (5 microM) or TTX (0.2 microM) and was thus identified as due to direct muscle stimulation. A train of 100 low intensity shocks gave a response with a longer latency (1.9 s) which was substantially sensitive to both prazosin and TTX; we assume this response is dominated by an indirect nerve-induced contraction. Relaxations, presumably caused by activation of circular muscle, were recorded from regions of some preparations both by direct and indirect stimulation. Noradrenaline (10-20 microM) induced a tonic contracture, spontaneous contractions and a large potentiation of the response to direct stimulation--but not to indirect stimulation implying a strong presynaptic inhibition. Noradrenaline also speeded the relaxation from contractions. Verapamil (1-100 microM) and nifedipine had no effect on the direct responses but verapamil (10 microM) inhibited the indirect response. Calcium removal prevented most, and 5 mM-EDTA all, of the direct response. However, even with EDTA, noradrenaline was able to support spontaneous and stimulus-induced contractions. Thus contraction of the vas, though sustained by external calcium, does not appear to directly depend on it.

Dengue virus-specific cross-reactive CD8+ human cytotoxic T lymphocytes

Stimulation with live dengue virus of peripheral blood mononuclear cells from a dengue virus type 4-immune donor generated virus-specific, serotype-cross-reactive, CD8+, class I-restricted cytotoxic T lymphocytes (CTL) capable of lysing dengue virus-infected cells and cells pulsed with dengue virus antigens of all four serotypes. These CTL lysed autologous fibroblasts infected with vaccinia virus-dengue virus recombinant viruses containing the E gene or several nonstructural dengue virus type 4 genes. These results demonstrate that both dengue virus structural and nonstructural proteins are targets for the cytotoxic T-cell-mediated immune response to dengue virus and suggest that serotype-cross-reactive CD8+ CTL may be important mediators of viral clearance and of virus-induced immunopathology during secondary dengue virus infections.

Mice immunized with recombinant vaccinia virus expressing dengue 4 virus structural proteins with or without nonstructural protein NS1 are protected against fatal dengue virus encephalitis

We have constructed vaccinia virus recombinants expressing dengue virus proteins from cloned DNA for use in experimental immunoprophylaxis. A recombinant virus containing a 4.0-kilobase DNA sequence that codes for three structural proteins, capsid (C), premembrane (pre-M), and envelope (E), and for nonstructural proteins NS1 and NS2a produced authentic pre-M, E, and NS1 in infected CV-1 cells. Mice immunized with this recombinant were protected against an intracerebral injection of 100 50% lethal doses of dengue 4 virus. A recombinant containing only genes C, pre-M, and E also induced solid resistance to challenge. Deletion of the putative C-terminal hydrophobic anchor of the E glycoprotein did not result in secretion of E from recombinant-virus-infected cells. Recombinants expressing only the E protein preceded by its own predicted N-terminal hydrophobic signal or by the signal of influenza A virus hemagglutinin or by the N-terminal 71 amino acids of the G glycoprotein of respiratory syncytial virus produced glycosylated E protein products of expected molecular sizes. These vaccinia virus recombinants also protected mice.

Role of ionizing irradiation for 393 keloids

Between 1928 and 1986, 393 keloid sites on 250 patients were presented. Three hundred seventy-five sites received superficial quality therapeutic irradiation. Etiologies were determined. The majority were excised prior to irradiation, and in these, histologic confirmation was obtained. Recurrence rate after irradiation was low, 9/375 (2.4%). When 7 of 9 recurrences are eliminated for post-irradiation ear lobe repiercing, true recurrence is only 2/375 (0.53%). Cosmetic result was considered excellent without recurrence in 92%; favorably improved with hypertrophic scar, nodule or altered pigment in 5.6%; and marginally improved with smaller, less symptomatic keloid in 2.4%. Significant complications were limited to persistent pigment disturbance in only 1 patient, and pre-irradiation hemorrhage in 1 patient (unrelated to radiotherapy). There was no wound dehiscence nor failure to heal irradiated incision site. Transient hyperpigmentation occurred in 91/375 (24%). Recurrence after irradiation was too rare to associate with etiology, specific technical factors, keloid configuration or velocity of initiating the post-operative radiotherapy. An unexpected finding was that 22/250 (9%) were Caucasian subjects. Our null (0%) carcinogenicity rate to date and the one-half of one percent true recurrence rate supports continued use of post-operative irradiation to prevent keloid formation in this group of documented troublesome keloid formers. Configuration subtypes are proposed, post-operative irradiation protocol is listed, and mechanism of action is explained in accordance with the dynamic pathophysiology of keloid.

Fatal food-induced anaphylaxis

Fatal food-induced anaphylaxis is rarely reported. In 16 months, we identified seven such cases involving five males and two females, aged 11 to 43 years. All victims were atopic with multiple prior anaphylactic episodes after ingestion of the incriminated food (peanut, four; pecan, one; crab, one; fish, one). In six cases the allergenic food was ingested away from home. Factors contributing to the severity of individual reactions included denial of symptoms, concomitant intake of alcohol, reliance on oral antihistamines alone to treat symptoms, and adrenal suppression by chronic glucocorticoid therapy for coexisting asthma. In no case was epinephrine administered immediately after onset of symptoms. Premortem or postmortem serum samples were available from six victims; in each case elevated levels of IgE antibodies to the incriminated food were demonstrated. Food-sensitive individuals must self-administer epinephrine promptly at the first sign of systemic reaction. Emergency care providers should be aware of cricothyrotomy as a life-saving procedure.

B-Ly1 cells: immortal Ly-1+ B lymphocyte cell lines spontaneously arising in murine splenic cultures

We have surveyed the molecular and functional properties of B-Ly1 cells, spontaneously occurring Ly-1+ cell tissue cultures lines established from murine spleen. Several features are surprising when compared to the conventional understanding of B cell physiology: In contrast to the major B cell subpopulation, these cells establish stable in vitro lines in the absence of nominal growth factors. This outgrowth is consistently accompanied by c-myc amplification and deregulation, and resistance to the effects of an autoregulatory IgM species which normally curtails the growth of B cells. These properties may be relevant to the disproportionate occurrence of Ly-1+ B cell malignancies in vivo. B-Ly1 cell lines consistently delete immunoglobulin constant region genes, and uniformly express lambda light chains, a rare murine isotype. These features may be causally related, and may reflect a novel recombinational activity (see this volume). Immunoglobulin expression can be modulated by conventional stimuli. However, the response is transient, and includes production of mature heavy chain isotypes ("class switching") without apparent switch deletion. Moreover, unstimulated B-Ly1 cells show transcriptional activity throughout the heavy chain locus, and a novel hypermutation activity affecting the immunoglobulin variable region. The mechanisms underlying this surprising pattern of immunoglobulin expression are unknown. However, one wonders whether this expression pattern, if common to Ly-1+ B cell in vivo, might provide modes to escape idiotypic or isotypic immunoregulation. If so, this may be relevant to the prevalence of autoantibody production by this subpopulation. Thus, we are hopeful that some of these unique properties, if confirmed in the Ly-1+ B cells in vivo, will provide more definitive markers for this subpopulation, and disclose mechanisms accounting for their distinctive physiology and pathophysiology.

Effects of bright incandescent light on seasonal and nonseasonal major depressive disorder

Previous research has indicated that exposure to bright fluorescent light can benefit clinically depressed individuals. The present study, a 1- to 2-week open trial of bright (greater than or equal to 2,000 lux) incandescent light with seasonal (fall/winter) and nonseasonal depressives, produced a therapeutic effect on seasonal depression, as measured by three criteria for recovery: final score on the Hamilton Rating Scale for Depression (HRSD) less than 10; final HRSD score less than or equal to 50% of pretreatment HRSD score; no longer meets DSM-III criteria for major depressive disorder. Phototherapy was not effective in the nonseasonal patients, whose functioning was more impaired than that of the seasonal subjects even before the trial. No adverse effects were observed in any patient.

Chemical estimation of fresh water immersion intervals

Postmortem vitreous humor chemistry studies were reviewed in 25 cases in which death was followed by submersion in fresh water for known lengths of time. The potassium concentrations in cold temperature cases initially increased in a linear manner, but appeared to level off or decline after about 1 week. In hot weather cases, potassium levels rose rapidly during the first few days postmortem. The sodium and chloride levels decreased in a fairly regular fashion, with less temperature variation. Increasing variation in values began to occur at about 7 days. The data show that dilution of the contents of the eye by fresh water begins at about that time in cases of cold water submersion. A formula employing the weighted average of the potassium and chloride concentrations can be used to determine the duration of submersion in cold water over the range of 2-10 days.

The eye as a chemical indicator of environmental temperature at the time of death

Vitreous humor chemistry profiles were reviewed on 133 autopsied cases in which death occurred outdoors during a six-year period, to determine whether environmental temperature at the time of death influenced chemistry values obtained at autopsy. The glucose concentration and total carbon dioxide content varied inversely with temperature. Values were significantly higher in the winter than the summer months. The mean glucose level was higher in deaths caused by cold exposure than in other deaths occurring in the cold, but individual cases could not be distinguished on the basis of chemistry values. Potassium levels tended to be slightly lower in winter. It was noted that chemistry studies could be used to help determine whether a body found outdoors in winter actually died in a different, warmer environment.

Evolution of a primary lymphoma of the orbit

A patient with a histologically benign lymphoid pseudotumour of the orbit developed a recurrent mass which proved to be a well differentiated lymphocytic lymphoma. Immunohistological studies showed that a majority of cells in the pseudotumour bore the same immunological markers as the subsequent lymphoma. There were no clinical or radiographic features of the initial lesion which indicated its eventual malignant course.

The effect of chilling, freezing, and rewarming on the postmortem chemistry of vitreous humor

The effect of chilling at the time of death on the postmortem chemistry of the vitreous humor was studied by using sheep heads obtained immediately following decapitation. One group of heads was kept at room temperature, while the remainder were chilled on ice or in ice water, then refrigerated or frozen. Vitreous humor specimens were taken at intervals over a 48-h period. Chilling inhibited the fall in the glucose concentration and the total carbon dioxide content and lessened the increase in lactic acid, compared to the room temperature group. Rapid glycolysis resumed when the heads rewarmed to room temperature starting at 6-h postmortem, but did not resume at later points. The rate of rise of the potassium and magnesium concentrations was also diminished in the chilled eyes. Freezing and thawing caused an abrupt increase in the potassium and magnesium levels, but other solutes were unaffected.