Epidemiology of inapparent and symptomatic acute dengue virus infection: a prospective study of primary school children in Kamphaeng Phet, Thailand

Dengue viruses are a major cause of morbidity in tropical and subtropical regions of the world. Knowledge about the epidemiology and host determinants of inapparent and severe dengue virus infections is limited. In this paper, the authors report findings from the first 3 years of a prospective study of dengue virus transmission and disease severity conducted in a cohort of 2,119 elementary school children in northern Thailand. A total of 717,106 person-school days were observed from 1998 to 2000. The incidence of inapparent and of symptomatic dengue virus infection was 4.3% and 3.6% in 1998, 3.2% and 3.3% in 1999, and 1.4% and 0.8% in 2000, respectively. Symptomatic dengue virus infection was responsible for 3.2%, 7.1%, and 1.1% of acute-illness school absences in 1998, 1999, and 2000, respectively. The early symptom complex of acute dengue virus infection is protean and difficult to distinguish from other causes of febrile childhood illnesses. The authors' results illustrate the spatial and temporal diversity of dengue virus infection and the burden of dengue disease in schoolchildren in Thailand. Their findings increase understanding of dengue virus transmission and disease severity in a well-defined cohort population and offer a study design in which to test the efficacy of potential dengue vaccines.

Dengue-specific T cell responses in peripheral blood mononuclear cells obtained prior to secondary dengue virus infections in Thai schoolchildren

Children who experience secondary dengue virus (DV) infections are at increased risk for dengue hemorrhagic fever. To study the effect of preexisting T cell responses to DV on the severity of secondary virus infection, peripheral blood mononuclear cells (PBMC) from 10 subsequently hospitalized and 12 nonhospitalized Thai schoolchildren were stimulated with inactivated dengue antigens, and proliferation of interferon (IFN)-gamma or tumor necrosis factor (TNF)-alpha responses of the preinfection PBMC were measured. Proliferation responses were observed in 11 subjects, and IFN-gamma responses were seen in 12 subjects, 6 of whom showed broad serotype cross-reactive IFN-gamma responses. TNF-alpha responses were detected exclusively in 4 hospitalized subjects. Four PBMC samples that showed neither proliferation nor cytokine responses to any dengue antigen were from nonhospitalized subjects. This study, thought to be the first to investigate T cell responses to DV in preinfection PBMC, suggests that the pattern of preexisting T cell responses influences the risk for severe disease.

Primary induction of human CD8+ cytotoxic T lymphocytes and interferon-gamma-producing T cells after smallpox vaccination

This study measured the ability of a standard smallpox vaccine, given by scarification (by bifurcated needle), to induce primary human vaccinia virus-specific cytotoxic and interferon (IFN)-gamma-producing T lymphocyte responses. Because protection against smallpox may be mediated in part by T cell memory responses induced by vaccination, an analysis of the induction of primary human cytotoxic T lymphocytes (CTL) and IFN-gamma-producing T cell responses was performed. Although smallpox is no longer an epidemic threat under natural conditions, vaccination is still recommended for persons working with vaccinia viruses in the laboratory and for those who may be at risk from the potential use of smallpox virus as a bioterrorism agent. The results demonstrate that smallpox vaccine given by bifurcated needle induces strong vaccinia virus-specific CD8(+) CTL and IFN-gamma-producing T cell responses and provide baseline information useful for planning the immunologic assessment of future smallpox vaccines.

T cell responses to an HLA-B*07-restricted epitope on the dengue NS3 protein correlate with disease severity

Dengue hemorrhagic fever (DHF), the severe manifestation of dengue virus (DV) infection characterized by plasma leakage, is more common in secondary DV infections in previously infected individuals and is associated with high levels of immune activation. To determine the Ag specificity of this immune response, we studied the response to an HLA-B*07-restricted T cell epitope, residues 221-232 of the DV NS3 protein, in 10 HLA-B*07(+) Thai children who were studied during and after acute DV infections. Peptide-specific T cells were detected in 9 of 10 subjects. The frequency of peptide-specific T cells was higher in subjects who had experienced DHF than in those who had experienced DF. We also detected peptide-specific T cells in PBMC obtained at the time of the acute DV infection in 2 of 5 subjects. These data suggest that the NS3 (221-232) epitope is an important target of CD8(+) T cells in secondary DV infection and that the activation and expansion of DV-specific T cells is greater in subjects with DHF than in those with dengue fever. These findings support the hypothesis that activation of DV-specific CD8(+) T cells plays an important role in the pathogenesis of DHF.

Increased production of interleukin-8 in primary human monocytes and in human epithelial and endothelial cell lines after dengue virus challenge

The more severe form of dengue virus infection, dengue hemorrhagic fever, is characterized by plasma leakage and derangements in hemostasis. As elevated interleukin-8 (IL-8) levels have been observed in sera from patients with more severe disease manifestations, a study was initiated to look at the effect of dengue virus infection in vitro on proinflammatory cytokine secretion and expression. A significant increase in IL-8 levels in the culture supernatant of primary human monocytes infected with dengue 2 virus (D2V) New Guinea C (NGC) was found by enzyme-linked immunosorbent assay. Additionally, by reverse transcriptase PCR, the mRNA was also augmented. Among the proinflammatory cytokines and their mRNAs measured (IL-6, IL-1 beta, IL-8, and tumor necrosis factor alpha), IL-8 showed the greatest change following D2V infection. Similarly, two cell lines, 293T (a human epithelial cell line) and ECV304 (an endothelial cell line), were permissive to D2V NGC and responded to the infection by increasing the synthesis of IL-8. Nuclear factor kappa B (NF-kappa B) and nuclear factor IL-6 (NFIL-6) are primary mediators of IL-8 expression. We studied the transcriptional regulation of IL-8 in the ECV304 and 293T cell lines and found that the induction of IL-8 gene expression involved the activation of NF-kappa B (P = 0.001) and, to a lesser extent, the activation of NFIL-6 in ECV304 cells only. We next observed by the chromatin immunoprecipitation procedure in vivo acetylation of core histones bound to the IL-8 promoter after D2V infection. IL-8 produced by infected monocytes and also IL-8 that may be produced by endothelial or other epithelial cells is associated with the hyperacetylation of histones bound to the IL-8 promoter in addition to the activation of transcription by NF-kappa B. We hypothesize that the overall increase in IL-8 synthesis observed in this in vitro study may play a role in the pathogenesis of the plasma leakage seen in dengue hemorrhagic fever and dengue shock syndrome.

Assessment of body fluid compartment volumes by multifrequency bioelectrical impedance spectroscopy in children with dengue

Dengue haemorrhagic fever (DHF), the most severe form of illness following infection with a dengue virus, is characterized by plasma leakage and a period of increased microvascular permeability. Monitoring of plasma volume and body fluid compartment shifts is an integral part of the clinical management of DHF, and is crucial to the performance of clinical research studies on DHF pathogenesis. Multifrequency bioelectrical impedance spectroscopy (BIS) was assessed as a non-invasive method to monitor body fluid compartment shifts in children participating in a prospective, hospital-based, study of dengue virus infections in Thailand. Over the 48 h surrounding defervescence, the extracellular water/intracellular water ratio (ECW/ICW) rose in children with dengue virus infections and correlated with increasing disease severity [DHF > intermediate dengue fever (DF)/DHF > DF]. Plasma leakage remained within the ECW compartment and was not directly measured by multifrequency BIS. Expansion of the ECW space in DHF appeared to be primarily due to diminished renal water clearance. During the course of dengue illness, multifrequency BIS did not improve on serial haematocrit and bodyweight determinations for monitoring plasma volume contraction and ECW expansion, respectively.

Cytokine gene expression and protein production in peripheral blood mononuclear cells of children with acute dengue virus infections

Plasma leakage in dengue hemorrhagic fever (DHF) is associated with elevated plasma levels of cytokines. To define further the contribution of immune activation to DHF and the source of cytokines, we analyzed the production of cytokines in peripheral blood mononuclear cells (PBMC) obtained from children with dengue, using RT-PCR and immunostaining. Tumor necrosis factor-alpha (TNF-alpha) and TNF-beta expression was detected in all samples by PCR and in < 50% of samples by immunostaining. Interferon-gamma (IFN-gamma) expression was detected in < 50% of samples by either method. Interleukin-2 (IL-2) and IL-4 expression was detected in a few samples by immunostaining but was not detectable by PCR. We found greater expression of TNF-alpha and IL-4 in DHF than in dengue fever or other (non-dengue) febrile illnesses. These results support the model of immunopathogenesis of DHF. However, low levels of cytokine expression in PBMC suggest that cellular activation in tissues may contribute to high serum cytokine levels in DHF.

Differing influences of virus burden and immune activation on disease severity in secondary dengue-3 virus infections

Dengue hemorrhagic fever (DHF), the most severe form of illness following infection with a dengue virus, is characterized by plasma leakage, thrombocytopenia, and hepatic inflammation. The interrelationships among virus burden, immune activation, and development of DHF were examined in 54 children with secondary dengue-3 virus infections participating in a prospective, hospital-based study. DHF was associated with higher mean plasma viremia early in illness and earlier peak plasma interferon-gamma levels. Maximum plasma viremia levels correlated with the degree of plasma leakage and thrombocytopenia. Maximum plasma levels of interleukin (IL)-10 and soluble tumor necrosis factor receptor-II correlated with the degree of thrombocytopenia, independently of viremia levels. Hepatic transaminase elevation correlated with plasma soluble IL-2 receptor levels and not with viremia levels. Quantitative differences in virus burden and host immune responses, and the timing of type 1 cytokine responses, have differing influences on the severity of disease manifestations during secondary dengue-3 virus infections.

Dose-related effects of smallpox vaccine

BACKGROUND

We conducted a double-blind, randomized trial of three dilutions of vaccinia virus vaccine in previously unimmunized adults in order to assess the clinical success rates, humoral responses, and virus-specific activity of cytotoxic T cells and interferon-gamma-producing T cells.

METHODS

Sixty healthy adults were inoculated intradermally by bifurcated needle with undiluted vaccine (dose, 10(7.8) plaque-forming units [pfu] per milliliter), a 1:10 dilution (dose, 10(6.5) pfu per milliliter), or a 1:100 dilution (dose, 10(5.0) pfu per milliliter); there were 20 subjects in each group. The subjects were monitored with respect to vesicle formation (an indicator of successful vaccination), the viral titer at the time of peak lesion formation, antiviral antibodies, and cellular immune responses.

RESULTS

A vaccinia vesicle developed in 19 of the 20 subjects who received undiluted vaccine (95 percent), 14 of the 20 who received the 1:10 dilution (70 percent), and 3 of the 20 who received the 1:100 dilution (15 percent). One month after vaccination, 34 of 36 subjects with vesicles had antibody responses, as compared with only 1 of 24 subjects without clinical evidence of vaccinia virus replication. Vigorous cytotoxic T-cell and interferon-gamma responses occurred in 94 percent of subjects with vesicles, and a cytotoxic T-cell response occurred in only one subject without a vesicle.

CONCLUSIONS

The vaccinia virus vaccine (which was produced in 1982 or earlier) still has substantial potency when administered by a bifurcated needle to previously unvaccinated adults. Diluting the vaccine reduces the rate of successful vaccination. The development of vesicular skin lesions after vaccination correlates with the induction of the antibody and T-cell responses that are considered essential for clearing vaccinia virus infections.

Generation of recombinant vaccinia viruses expressing Puumala virus proteins and use in isolating cytotoxic T cells specific for Puumala virus

Puumala (PUU) virus causes a form of hemorrhagic fever with renal syndrome (HFRS), called nephropathia epidemica (NE), in Europe. HFRS is characterized by an increased capillary permeability, which we hypothesize is caused by hyperactivation of the host immune system, especially cellular immune responses. To identify cytotoxic T lymphocytes (CTLs) specific for the PUU virus from NE patients, we have made recombinant vaccinia viruses expressing PUU virus proteins, the nucleocapsid (N) and two surface glycoproteins, G1 and G2. Recombinant vaccinia viruses carrying the N or the first half of the G2 cDNA under the control of a strong synthetic promoter were made. To express G1 and the second half of the G2 proteins, however, we needed to use a T7 expression system, where the T7 RNA polymerase is produced from another recombinant vaccinia virus co-infecting the same cells. These recombinant vaccinia viruses were used to detect and clone PUU virus-specific CTLs from the peripheral blood mononuclear cells of NE patients. An HLA-A24-restricted CTL line recognizing the G2 protein was isolated and its 9-mer epitope was determined.

Human cytotoxic T lymphocyte responses to live attenuated 17D yellow fever vaccine: identification of HLA-B35-restricted CTL epitopes on nonstructural proteins NS1, NS2b, NS3, and the structural protein E

Yellow fever virus (YFV) is a re-emerging problem despite the existence of an effective live-attenuated vaccine. The induction of YFV-neutralizing antibodies undoubtedly contributes to vaccine efficacy, but T lymphocyte responses to YFV likely play a role in long-term efficacy. We studied the T lymphocyte responses to YFV in four vaccinees. Proliferation and cytolytic responses to YFV were demonstrated in all subjects. We isolated 13 YFV-specific CD8(+) CTL lines that recognized epitopes on the E, NS1, NS2b, and NS3 proteins; eight CTL lines were HLA-B35-restricted. YFV-specific T cell responses were detectable by IFN gamma ELISPOT assays 14 days postvaccination, with T cell frequencies sustained for up to 19 months. To our knowledge, this is the first report of human T lymphocyte responses following YFV vaccination. These results indicate that the live 17D YFV vaccine induced CD8(+) T cell responses directed against at least four different HLA-B35-restricted YFV epitopes.

Binocular summation for grating detection and resolution in foveal and peripheral vision

Peripheral monocular grating resolution has been shown to be limited by the sampling density of the underlying retinal ganglion cells. We wanted to determine if peripheral resolution is also sampling limited binocularly; and, if so, how great is any improvement in either detection or resolution when viewing binocularly? We measured detection and resolution acuity for sinusoidal gratings in foveal and peripheral vision both monocularly and binocularly. Detection and resolution acuity were very similar in foveal vision and displayed a binocular improvement of 5% over best monocular acuity. However, in peripheral vision, while detection acuity improved by 6% binocularly, resolution acuity improved by 16%, with a subsequently smaller aliasing zone. This improvement was greater than predicted by probability summation and implies that the two monocular ganglion cell sampling arrays combine at a higher level resulting in a higher binocular sampling density.

MIP-1 alpha and MIP-1 beta induction by dengue virus

Dengue virus (DV) infection can result in either a mild febrile illness known as dengue fever (DF) or a life-threatening disease called dengue hemorrhagic fever (DHF). DHF is more prevalent in patients undergoing secondary DV infection. This observation has led to the hypothesis that DHF may be the result of immune reactions to the secondary DV infection; an event termed immunopathology. Two cellular factors, MIP-1 alpha and MIP-1 beta, have been found to be induced by infection with DV. MIP-1 induction by DV infection was observed in a myelomonocytic cell line, as well as in peripheral blood mononuclear cells isolated from a dengue naive donor. MIP-1 induction was not due to factors secreted by infected cells. In fact, replication-competent virus was required to induce MIP-1. Evidence is also provided that MIP-1 genes are expressed in patients with dengue disease. It is hypothesized that these chemokines may have roles in the immunopathology of dengue infections and may contribute to fever and bone marrow suppression observed in patients with DV infections.

Induction of T lymphocyte responses to dengue virus by a candidate tetravalent live attenuated dengue virus vaccine

Development of a safe and immunogenic tetravalent dengue virus (DV) vaccine has been designated as a priority by the World Health Organization. We characterized the T cell response to DV induced by a candidate live attenuated tetravalent DV vaccine as part of a phase I study. Proliferation and cytotoxic T lymphocyte (CTL) responses to multiple DV serotypes were detected in six of six and four of four subjects studied, respectively. Proliferation responses were higher to DV serotypes 1 and 3 than to serotypes 2 and 4. CTL responses were higher to DV serotypes 2 and 3 than to serotype 1, and included serotype cross-reactive responses. Production of interferon-gamma, but not IL-4, was observed in response to DV stimulation. This candidate vaccine is immunogenic for both CD4+ and CD8+ T lymphocytes. However, T cell responses to the four DV serotypes were not equivalent, suggesting that the vaccine could be further optimized.

Three double-blind, randomized trials evaluating the safety and tolerance of different formulations of the saponin adjuvant QS-21

The effects of the adjuvant QS-21 in various formulations on immediate pain on injection after intramuscular injection were evaluated in three Phase I clinical trials in healthy adults. Each trial was designed as a double-blind, randomized, four-way or five-way cross-over study with each subject acting as his/her own control. In the first trial, four formulations designed to evaluate the effect of QS-21 or pH (over a range of 6--7.2) were evaluated: phosphate-buffered saline at pH 6.0 or 7.2, and 50 microg of QS-21 in phosphate-buffered saline at pH 6.0 or 7.2. Thirty-three volunteers received each of the four intramuscular injections in random order separated by approximately 1 week. The volunteers assessed the immediate injection pain from 0 to 10 (none to most pain). The data indicate that the presence of QS-21, but not pH, is associated with transient injection site pain. The second trial, which utilized the same design as the first trial, evaluated formulations of QS-21 in various excipients. Fifteen volunteers received phosphate-buffered saline, QS-21/PBS, QS-21/aluminum hydroxide, and QS-21/4 mg/ml of polysorbate 80. Polysorbate 80, but not aluminum hydroxide, reduced the mean pain score compared to QS-21/PBS. The third trial evaluated formulations of QS-21 in additional excipients. Fifteen volunteers received aluminum hydroxide (without QS-21), QS-21/PBS, QS-21/0.72% benzyl alcohol, QS-21/30 mg/ml of hydroxypropyl-beta-cyclodextrin, and QS-21/8-mg/ml of polysorbate 80. Benzyl alcohol, cyclodextrin, and the higher concentration of polysorbate 80 reduced the pain scores associated with QS-21. Hence, QS-21 is associated with injection pain in simple buffer formulations, but it is possible to improve the acceptability of QS-21-containing formulations through reformulation with certain excipients.

Human dendritic cells are activated by dengue virus infection: enhancement by gamma interferon and implications for disease pathogenesis

The ability of dendritic cells (DCs) to shape the adaptive immune response to viral infection is mediated largely by their maturation and activation state as determined by the surface expression of HLA molecules, costimulatory molecules, and cytokine production. Dengue is an emerging arboviral disease where the severity of illness is influenced by the adaptive immune response to the virus. In this report, we have demonstrated that dengue virus infects and replicates in immature human myeloid DCs. Exposure to live dengue virus led to maturation and activation of both the infected and surrounding, uninfected DCs and stimulated production of tumor necrosis factor alpha (TNF-alpha) and alpha interferon (IFN-alpha). Activation of the dengue virus-infected DCs was blunted compared to the surrounding, uninfected DCs, and dengue virus infection induced low-level release of interleukin-12 p70 (IL-12 p70), a key cytokine in the development of cell-mediated immunity (CMI). Upon the addition of IFN-gamma, there was enhanced activation of dengue virus-infected DCs and enhanced dengue virus-induced IL-12 p70 release. The data suggest a model whereby DCs are the early, primary target of dengue virus in natural infection and the vigor of CMI is modulated by the relative presence or absence of IFN-gamma in the microenvironment surrounding the virus-infected DCs. These findings are relevant to understanding the pathogenesis of dengue hemorrhagic fever and the design of new vaccination and therapeutic strategies.

T cell activation in vivo by dengue virus infection

It is accepted that T cells play a critical role during virus infections; however, T cell responses in vivo in acute stage of virus infection are not understood. We examined T cell activation in vivo in two volunteers who developed dengue fever in response to vaccination with a candidate live dengue vaccine. Serial plasma collected from the volunteers from day 0 (before infection) to day 17 after infection were examined for levels of soluble interleukin-2 receptor (sIL-2R), soluble CD4 (sCD4), soluble CD8 (sCD8), interleukin-2 (IL-2) and interferon gamma (INF gamma). Elevation of the levels of sIL-2R, IFN gamma, sCD4 and IL-2 became obvious during the period of viremia and was followed by a later increase in the level of sCD8. The levels of IFN gamma and sIL-2R declined after the end of the period of viremia. These results indicate that i. T cells are activated in vivo by dengue virus infection ii. activation of CD4+ T cells occurs during the period of viremia iii. activation of CD8+ T cells follows CD4+ T cell activation. These results suggest that activation of T cells in vivo may contribute to controlling acute dengue virus infections.

Foveal and peripheral thresholds for detection and resolution of vanishing optotype tumbling E's

We measured detection and resolution acuity for vanishing optotype tumbling E stimuli in both the fovea and at 30 degrees in the periphery to determine if peripheral resolution is sampling limited for this stimulus. In the fovea, where acuity is optically limited, detection and resolution were the same. At 30 degrees, however, detection was markedly better than resolution indicating that peripheral resolution is sampling limited for this stimulus. Detection acuity was higher when contrast was 90% rather than 40%, but resolution did not change with contrast. The vanishing optotype is a legitimate perimetric stimulus to measure retinal ganglion cell density provided the task is resolution and not detection.

Effect of localized defocus on detection thresholds for different sized targets in the fovea and periphery

PURPOSE

Previous studies of optical blur in perimetry have measured the effect of foveal refractive error on peripheral perimetric detection thresholds. Since peripheral refractive error can be significantly different from that of the fovea we wished to remove the ambiguity of previous results by correcting the actual peripheral refractive error first before adding blur.

METHODS

We measured detection thresholds in the fovea and at 30 degrees in the horizontal temporal field in two trained observers. Peripheral refractive error was determined at each location and thresholds measured at the same locations for stimuli ranging in size from 0.2 to 6.4 degrees and refractive errors between +/-4.00 diopters.

RESULTS

Foveal thresholds increased immediately with increasing refractive error, particularly for smaller stimulus sizes. At 30 degrees, thresholds for smaller stimuli were less affected by defocus initially and then increased more sharply. Larger stimuli were relatively unaffected by defocus such that when stimulus size reached 1.6 degrees there was little or no increase in threshold for refractive error between +/-4.00 diopters.

CONCLUSIONS

Peripheral refractive error, largely forgotten by perimetrists, has a significant effect on performance, particularly for smaller stimuli. Differences in foveal vs peripheral viewing can be explained by differences in ganglion cell receptive field sizes.

Analysis of plasma viral RNA levels during acute dengue virus infection using quantitative competitor reverse transcription-polymerase chain reaction

There is increasing recognition of the potential importance of viral burden in the pathogenesis of dengue hemorrhagic fever (DHF). There is little data available, however, describing the kinetics of viral replication in humans with natural dengue virus (DV) infection. Standard procedures for measuring titers of infectious virus in clinical specimens are either laborious or insensitive. We developed a method for measurement of DV RNA in plasma samples based on reverse transcription-polymerase chain reaction (RT-PCR) using a mutant RNA target as a competitor. This technique was reproducible and accurate for samples containing any of the four DV serotypes, and could be applied to samples containing as few as 250 copies of RNA per reaction. We examined plasma viral RNA levels in 80 children with acute DV infection; sequential plasma samples were tested in 34 of these children. Plasma viral RNA levels ranged as high as 10(9) RNA copies/ml, and correlated with titers of infectious virus measured in mosquitoes (r= 0.69). Plasma viral RNA levels fell rapidly during the last several days of the febrile period. We did not find a significant difference in maximal plasma viral RNA levels between children with DHF and children with dengue fever, but peak viral RNA levels were identified in only 16 subjects. We conclude that this quantitative RT-PCR method will be valuable for further studies of natural DV infections.

T cell receptor Vbeta gene usage in Thai children with dengue virus infection

T lymphocyte activation during dengue is thought to contribute to the pathogenesis of dengue hemorrhagic fever (DHF). We examined the T cell receptor Vbeta gene usage by a reverse transcriptase-polymerase chain reaction assay during infection and after recovery in 13 children with DHF and 13 children with dengue fever (DF). There was no deletion of specific Vbeta gene families. We detected significant expansions in usage of single Vbeta families in six subjects with DHF and three subjects with DF over the course of infection, but these did not show an association with clinical diagnosis, viral serotype, or HLA alleles. Differences in Vbeta gene usage between subjects with DHF and subjects with DF were of borderline significance. These data suggest that the differences in T cell activation in DHF and DF are quantitative rather than qualitative and that T cells are activated by conventional antigen(s) and not a viral superantigen.

Transient decreases in human T cell proliferative responses following vaccinia immunization

To further study the immunosuppression associated with virus infections, we analyzed the proliferative responses of serial PBMC samples obtained following vaccinia virus immunization. In four of five volunteers, responses to PHA, anti-CD3, vaccinia virus, and recall antigens were markedly decreased at at least one time point between days 5 and 29 after vaccination. Responses to PHA were restored by the addition of IL-2 or irradiated autologous healthy PBMC in the two volunteers tested, suggesting that the proliferation defect is attributable to accessory cell dysfunction. In one donor, immobilized anti-CD3 failed to induce proliferation, but addition of immobilized anti-CD28 partially restored proliferation. These results indicate that vaccinia virus infection can transiently suppress proliferative responses of PBMC, in part by causing accessory cell dysfunction. Our findings extend the list of viral infections associated with systemic immunologic effects and demonstrate that suppression of proliferation can occur with localized virus infections.

Aliasing in peripheral vision for flickering gratings under different levels of illumination

PURPOSE

To assess how far retinal illumination can be reduced for sine-wave gratings phase reversing at different temporal frequencies in peripheral vision, while maintaining sampling limited resolution acuity performance, as evidenced by an aliasing zone between detection and resolution.

METHODS

Computer generated sine wave gratings were presented with flicker rates from 0 to 40 Hz under retinal illumination levels of 3.5 to -0.5 log trolands. Resolution and detection thresholds were measured at 30 degrees in the horizontal temporal field using a spatial and temporal 2AFC paradigm respectively.

RESULTS

At high illumination levels, detection acuity is higher than resolution acuity between 0 and 40 Hz indicating that resolution is sampling limited. As illumination level decreases the aliasing zone becomes narrower, especially at high temporal frequency until it disappears completely at 0.5 log trolands.

CONCLUSIONS

Peripheral resolution acuity ceases to be sampling limited below 1.5 log trolands for low temporal frequency gratings and at higher levels for high temporal frequency gratings. Sampling limited acuity was recorded for high frequency gratings under higher illumination levels which could be mediated by the M cells alone, but this is not the case for the lower levels of illumination.

Dengue viremia titer, antibody response pattern, and virus serotype correlate with disease severity

Viremia titers in serial plasma samples from 168 children with acute dengue virus infection who were enrolled in a prospective study at 2 hospitals in Thailand were examined to determine the role of virus load in the pathogenesis of dengue hemorrhagic fever (DHF). The infecting virus serotype was identified for 165 patients (DEN-1, 46 patients; DEN-2, 47 patients; DEN-3, 47 patients, DEN-4, 25 patients). Patients with DEN-2 infections experienced more severe disease than those infected with other serotypes. Eighty-one percent of patients experienced a secondary dengue virus infection that was associated with more severe disease. Viremia titers were determined for 41 DEN-1 and 46 DEN-2 patients. Higher peak titers were associated with increased disease severity for the 31 patients with a peak titer identified (mean titer of 107.6 for those with dengue fever vs. 108.5 for patients with DHF, P=.01). Increased dengue disease severity correlated with high viremia titer, secondary dengue virus infection, and DEN-2 virus type.

High levels of viremia in patients with the Hantavirus pulmonary syndrome

Hantavirus pulmonary syndrome (HPS) is a rare but acute fulminant disease caused by Sin Nombre virus (SNV). To understand the role of the viral load in the pathogenesis of HPS, the load of virus in the blood of patients with HPS was measured. A quantitative reverse transcription-polymerase chain reaction assay was developed for SNV, because SNV is difficult to grow in cell culture. Thirty-eight samples from 26 patients with HPS were analyzed. Twenty of the 26 initial samples were positive for viral RNA (7 of 9 samples were obtained from patients with fatal cases, and 13 of 17 were obtained from survivors). Mean viral RNA copy numbers were 106.1+/-1.4/mL in positive cases (106.7+/-1.4/mL in fatal cases, 105.8+/-1.3/mL in survivors) and were correlated with peak hematocrit (P<.05) and with the lowest platelet count (P=.05). In 8 survivors who had serial samples obtained, viral RNA copy numbers decreased promptly after resolution of fever.