Dengue virus specific T cell responses to live attenuated monovalent dengue-2 and tetravalent dengue vaccines.

The proliferative T cell responses to dengue vaccines were studied using the parental strains of dengue vaccines as antigens in 26 dengue immune individuals who resided in Bangkok which is the endemic area of dengue infection. The magnitude of the T cell responses in subjects with flavivirus cross-reactive neutralizing antibody was much higher and the cross-reactivity was broader than in those with dengue serotype-specific neutralizing antibodies, Japanese encephalitis (JE) specific antibodies or dengue cross-reactive antibodies. The T cell response in those with neutralizing antibody against a single serotype or in those who had dengue cross-reactive neutralizing antibody was relatively low, independent of the level or degree of cross-reactivity of the antibody. Evaluation of the proliferative T cell responses in 8 recipients of the monovalent dengue-2 (16681-PDK53) or the tetravalent dengue vaccines demonstrated that both vaccines induced high levels of neutralizing antibody as well as high levels of T cell responses to all serotypes of dengue virus. These results indicate that the evaluated dengue vaccines efficiently induced humoral and cell mediated immunity comparable to natural infection with dengue virus.

Possible evidence of endothelial cell activation and disturbance in thalassemia: an in vitro study.

Activation of vascular endothelium is considered as an important facet of inflammation, thrombosis, and vasculitis. Activated endothelial cells express a number of immunologically relevant surface markers which are not detected in dormant condition. These surface markers on endothelial cell may involve in adhesion reaction and migration of blood cell components. We demonstrated increased level of the soluble adhesion molecules in circulating blood of both alpha- and beta-thalassemic patients. These adhesion molecules are theoretically known to be released from endothelial cells. The adhesion molecules included soluble Intercellular Adhesion Molecule-1 (sICAM-1), soluble E-Selectin (ELAM-1), soluble Vascular Cell Adhesion Molecule-1 (sVCAM-1), and von Willebrand Factor (vWF). The levels of these adhesion molecules were measured in serum from 32 thalassemic patients and 10 control healthy subjects. As compared to normal, increased sICAM-1 was found in beta-thal/HbE patients with non-splenectomy; BE-NS (p = 0.002), increased ELAM-1 in beta-thal/HbE patients with splenectomy; BE-S (p = 0.01) and HbH with Hb Constant Spring; HbH/CS (p = 0.001), and increased sVCAM-1 in BE-NS; (p = < 0.0001) and BE-S (p = 0.002). Significant increase in von Willebrand Factor (vWF), a marker for endothelial cell, was shown in BE-S (p = 0.04) as compared to normal. Adhesion molecules were also markedly demonstrated in the supernatant of in vitro culture of human vascular endothelial cell in the presence of 30% thalassemic serum, and these adhesion molecules were also detected on the surface of the cells by using the technic of laser scanning confocal microscope and direct immunofluorescence.

Dengue viruses induce cell proliferation and morphological changes of endothelial cells.

Replication of dengue viruses (type 1, 2, 3 and 4) in vitro in endothelial cells from human umbilical cord vein was demonstrated by virus titers and immunofluorescent antibody studies. Both showed highest peak at Day 6 after inoculation and declined to origin at Day 14. Some of the cultured endothelial cells detached from the culture well. Most of these floating cells were rarely viable as shown by failure in trypan blue exclusion whereas the adhering cells are mostly viable. More frequent and higher intensity of immunofluorescent positive cells were found in the detached cells as compared to adhering cells. The virus titers in the supernatant and in the adhering cell population were comparable, although floating cells were maximally 26.2% of the total cultured endothelial cells. Many floating cells and occasional adhering cells had numerous blebs on their surface. Endothelial cell proliferation was markedly increased after virus inoculation as compared with the control. Increased number of mitotic cells was also observed in the dengue virus-endothelial cell culture. Comparing among the four types, dengue type 4 induced highest peaks of cell proliferation and cell mitosis at Day 10 after inoculation. Dengue type 2 had the highest virus titers both in adhering cells and in supernatant at Day 6 as compared with other types.

Immunohistochemical characterization of a new monoclonal antibody reactive with dengue virus-infected cells in frozen tissue using immunoperoxidase technique.

This paper presents a novel monoclonal antibody shown to react with cytoplasmic antigens in various dengue infected human frozen organs from autopsy and necropsy specimens. Strong reactivity was found in hematopoietic cells, including immunoblasts, lymphocytes, plasma cells and macrophages of spleen, lymph node, lung, kidney and stomach. Strikingly, strong positivity was demonstrated in cerebral cortex neurones, Purkinje cells, choroid plexus and blood vessels in addition to astrocytes and microglia. Neurotropism of the virus could explain the meningitis, encephalitis, mononeuropathy and polyneuropathy observed by direct toxicity, but noted especially after an activation of mononuclear phagocytes and amplification of the immune response with subsequent vascular inflammation and formation of immune complexes.

In vivo and in vitro studies on the morphological change in the monkey epidermal Langerhans cells following exposure to dengue 2 (16681) virus.

A direct comparison of skin Langerhans cell (LC) morphologic change following in vivo and in vitro exposure to dengue-2 (DEN-2) virus (16681) was performed in the monkey to investigate any differences in functional activity profiles. Time-lapse study of skin biopsy at the intradermal (id) virus injection sites, and thin skin sheets removed from the monkey with exposure to virus in culture medium, revealed a highly active migration of epidermal LCs in both sets of experimental specimens. The migration led to a relatively higher number of dendritic cells (DC) which appeared in active migrational profiles, in the superficial dermis. Moreover, obvious cytoplasmic structural changes, corresponding to their immunologic function, were observed in these superficial dermal DCs 2 hours after exposure. Despite their similar changes, early and late endosomes with degraded virus-like particles could be seen in the skin sheets owing to lagging in cellular physiological process in vitro, but none in the skin biopsies. Existence of these endosomes, which was extremely difficult to visualize in vivo, highlighted the mode of antigen processing by the endocytic pathway. The present study showed that the epidermal LC was a potent antigen-presenting cell for eliciting the success of id immunization and carried out the immunological activity in vivo or in vitro in the like manner, in respect to the physiological conditions.

Dengue-3 (16562) PGMK 33 vaccine: neurovirulence, viremia and immune responses in Macaca fascicularis.

Investigation of monkey neurovirulence of dengue-3 viruses (DEN-3, 16562) was undertaken to provide an evaluation of the relative safety of virus strain attenuated for potential use of live virus vaccine. Ten flavivirus-negative, cynomolgus monkeys (Macacafascicularis) were used in the test. The animals were inoculated intrathalamically, intraspinally and intramuscularly with DEN-3 PGMK 33 attenuated live virus vaccine (6 monkeys): parent virus (2) and control cell culture fluid (2). Blood samples were collected on days 0, 1, 2, 4, 6, 8, 10, 12 and 21 for virus isolation and days 0 and 21 or 22 for serologic testing. One monkey with DEN-3 (16562) PGMK 33 candidate vaccine had detectable viremia on day 10. By day 21, all recipients of PGMK 33 and both monkeys with DEN-3 parent virus developed serum neutralizing antibodies to DEN-3 titers ranged from 56-320. The monkeys showed no evidence of illness and none died of dengue infection. Histopathological examination of tissue collected on day 21 or 22 revealed only minimal neurovirulence lesions as scored by the routine grading system. No differences were observed between the DEN-3 parent and vaccine viruses and it is concluded that neither virus is neurovirulent for cynomolgus monkeys.

Dengue virus and endothelial cell: a related phenomenon to thrombocytopenia and granulocytopenia in dengue hemorrhagic fever.

Adhesion to endothelial cells by blood cells was assessed by measuring the cell number of each blood cell component in the supernatant after exposing blood cells to dengue-infected endothelial cells for 0, 10, 20 and 30 minutes. White blood cells, neutrophils, lymphocytes, platelets, and large lymphocytes or large unstained cells (LUC) preferentially bound to dengue-infected endothelial cells as compared to the control endothelial cells. P values were 0.0096 for total leukocytes and platelets, 0.006 for lymphocytes, and 0.001 for neutrophils and LUC. Monocytes basophils and eosinophils had no interaction with dengue-infected endothelial cells. The increased binding of neutrophil and platelet to endothelial cell may explain neutropenia and thrombocytopenia in DHF patients.

Immune response in rabbits to dengue viral proteins.

Antisera to all types of dengue and Japanese encephalitis (JE) viruses were raised in rabbits. The first set of rabbits was immunized with crude antigens prepared by a sucrose acetone extraction. The first generation of antisera demonstrated antibody activity towards the group specific flaviviruses, without unwanted antibody activity towards the mouse brain material. Antibody activity towards E, NS3, NS5 and NS1 could be observed by western blot/immunoenzymatic assay. Another set of rabbits was immunized with the precipitin complexes formed between antisera raised against each type of dengue, or JE viruses, and their homologous antigens. Each rabbit serum was screened again by the western blot/immunoenzymatic method, and was absorbed with other types of dengue viruses until the specific activity towards the immunized viral antigen was obtained. The last 2 bands detected on the viral antigen strip were the doublet of protein bands at Mr 67 and 71 kDa, which are the NS3 protein. The specific polyclonal antisera obtained can be used with other tests as well as the monoclonal antibody. Since absorption can lead to type specific antisera, this NS3 protein must be quite unique, it processes a type specific determinant (s) and deserves further study as a target molecule at the polypeptide level as well as at the RNA level.

Dengue virus serotypic identification using suckling mouse and western blot technique.

The suckling mouse which is used in the classical method to detect and propagate dengue viruses was evaluated in conjunction with the western blot and immunoenzymatic methods to detect the infecting strains of dengue viruses. After intracerebral inoculation of patients' sera into the suckling mice for 7 days, the mice were examined for the presence of dengue proteins, even though the mice did not have the neurological symptoms which usually serve as an indicator for the presence of dengue infection in the mouse brain. With a blind study of a set of 12 specimens, the suckling mice could detect the virus with the same frequency as the mosquito system but in shorter time of incubation period. The whole process to identify the type of infection takes 9 days. Another important finding is the demonstration of the virion antigen in the liver. The quantity and quality of viral proteins in liver are comparable to those in the brain suggesting that the virus may replicate in the liver as well as in the brain.

Antibodies to dengue viral polypeptides. I. Sensitivity and specificity of the viral-antigen-strips/enzymeimmunoassay (VAS/EIA).

The authors applied polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE), western blot, and enzymeimmunoassay (EIA) for the detection of antibodies toward individual dengue viral proteins or polypeptides. SDS-PAGE procedure as described by Laemmli et al., was applied and modified. The results can be observed by visualization. The scores, from 0 to 4, can be assigned by comparing the intensity of the color development. Besides being sensitive and rapid, this technique yields information of the polypeptides or molecular level. An increasing of intensities of positive reactions indicated rising in antibodies titers and all serotypes of dengue viruses (from type 1 to type 4) can be tested together allowing reliable comparison among serotypes. With hyperimmune human sera, at least 13 polypeptides reacted with sera while negative non-immune subject showed no reaction. It is highly possible to use this technique as a rapid quantitative and for qualitative analysis of antibodies to individual viral proteins as well.

Application of peroxidase-antiperoxidase (PAP) staining for detection and localization of dengue-2 viral antigen. II. Observations for the antibody enhancement activity in human monocytes.

Peroxidase-antiperoxidase (PAP) staining was applied to measure the antibody enhancement activity in human monocytes. Increasing in number of infected cells can be seen with increasing of staining intensity of the cells by ordinary light microscope. Shifting of the optimum enhancement activity was found in previously tritiated antiserum indicated that for titration of antibody enhancement activity several dilutions of antiserum should be included in each experiment. Validity of the PAP method was made by the comparison of the results with Infectious Center Assay (ICA). With this technique, titration for antibody enhancement for dengue virus infection can be done with non-expensive equipment and can be kept for comparison for months.

Neurovirulence effects of dengue-2 viruses on the rhesus (Macaca mulatta) brain and spinal cord.

Vaccines prepared from attenuated virus can cause symptomatic viral infection of the central nervous system. In the present study, dengue-2 parental and its live attenuated viruses were tested by intrathalamic and intraspinal injections in rhesus monkeys. The dengue-2 viruses were found to be only very weakly neurovirulent when injected directly into the brain or spinal cord of rhesus monkeys.

The neurovirulence of flaviviruses in crab-eating monkeys (Macaca fascicularis).

The neurovirulent properties of attenuated dengue-2 and yellow fever (YF) vaccines, dengue-2 (DEN-2) and Japanese encephalitis (JE) viruses were studied in crab-eating monkeys (Macaca fascicularis). Number of central nervous system sites (as proportion affected) with neurovirulence (NV) lesions were compared. The results indicate that these monkeys reliably developed NV-lesion when inoculated with either JE or YF vaccine viruses (87%). NV-lesions occurred in a minority when inoculated with DEN-2 vaccine virus, were of minimal severity (9%), were probably biologically insignificant, and were of equal or less severity than lesions produced by its parental virus (10%).

Blood value changes in flavivirus-inoculated Macaca fascicularis monkeys.

Blood values were analysed in eighteen cynomolgus monkeys on pre-and post-neurovirulence testing of dengue-2 and yellow fever vaccine viruses, dengue-2 parental and Japanese encephalitis viruses. Certain changes between blood chemistry, hematology and serology were observed and briefly discussed.

Precipitating antibodies to non-treated dengue type 2 viral antigens in sera of Thai hemorrhagic fever patients by crossed immunoelectrophoresis.

Crossed immunoelectrophoresis of dengue type 2 virus revealed at least two precipitating antigens which shared some antigenic determinants. Glycoprotein components of both antigens were detected by binding to concanavalin A. Sera from dengue hemorrhagic fever patients showed precipitating antibodies to both antigens which could be quantitated according to the precipitate patterns formed in the intermediate gel of crossed immunoelectrophoresis. All secondary dengue hemorrhagic fever patients demonstrated an increase in precipitin titers in convalescence sera. Most patients with mild illness contained precipitating antibodies in acute phase sera whereas severe cases did not. Convalescent sera from severe cases showed only low titers. These precipitating antibodies may be associated with protection since they were produced early only in those with mild form of illness.

Application of peroxidase-antiperoxidase (PAP) staining for detection and localization of dengue-2 antigen. I. In an endogenous peroxidase containing cell systems.

The unlabelled immunoperoxidase, peroxidase-anti-peroxidase (PAP), technique was used to detect dengue type-2 viral antigen in several cell systems including the endogenous peroxidase containing cells. These cells are the mosquito cell line (C6/36), continuous cell line of rhesus monkey kidney (LLC-MK2), human monocyte culture both cell suspension and monolayer, and human peripheral blood leukocytes. All of these specimens gave the same results that dengue-2 viral antigen presented in cytoplasm only and the patterns of marker presentation in positive cells varied depending on the duration after infection. The sensitivity of this method is extremely high since it can detect dengue-2 antigen after its attachment on mosquito cells (15 min) as seen in experiments with mosquito cell line, C6/36. False positive was not observed in all cell systems tested.

Electron microscopic study of the vascular endothelial cell in dengue hemorrhagic fever.

Electron microscopic studies were performed from skin biopsies taken from patients aged between 1-14 years suffering from dengue hemorrhagic fever. Several capillaries showed marked distortion, but severely damaged vessels were not observed in this study. In many cases, however, swelling of a single endothelial cell was noted. This was characterized by a rarefaction of the cytoplasm and formation of the plasma membrane which extruded into lumen and narrowed it. In many vessels examined, these blebs became detached from the endothelium and were found free within the capillary lumen. Myelin figures were often observed in such vessels. Mitochondria in the swollen endothelial cells often showed contraction of the inner compartments. Although, most of the endothelial junctional complexes were intact, several gap formations, in vascular wall were observed. Vacuolation of the cytoplasm and increase in the pinocytotic vesicles in endothelial cells which represented transport of plasma fluids from the capillary to the pericapillary space were quite evident. In no case did there seem to be marked alternation of the basement membrane of the capillary. The morphological alterations observed in this study only suggest the non-specific response of the dermal capillaries. These findings were similar to the findings observed in capillaries after being subjected to heat or ischemia.