IMMUNITY TO YELLOW FEVER ENCEPHALITIS OF MONKEYS AND MICE IMMUNIZED BY NEURAL AND EXTRANEURAL ROUTES

Innovative in cellulo method as an alternative to in vivo neurovirulence test for the characterization and quality control of human live Yellow Fever virus vaccines: A pilot study

Live attenuated vaccines have proved to be mostly valuable in the prevention of infectious diseases in humans, especially in developing countries. The safety and potency of vaccine, and the consistency of vaccine batch-to-batch manufacturing, must be proven before being administrated to humans. For now, the tests used to control vaccine safety largely involve animal testing. For live viral vaccines, regulations require suppliers to demonstrate the absence of neurovirulence in animals, principally in non-human primates and mice. In a search to reduce the use of animals and embracing the 3Rs principles (Replacement, Reduction, Refinement in the use of laboratory animals), we developed a new Blood-Brain Barrier Minibrain (BBB-Minibrain) in cellulo device to evaluate the neuroinvasiveness/neurovirulence of live Yellow Fever virus (YFV) vaccines. A pilot study was performed using the features of two distinct YFV strains, with the ultimate goal of proposing a companion test to characterize YFV neurovirulence. Here, we demonstrate that the BBB-Minibrain model is a promising alternative to consider for future replacement of YFV vaccine in vivo neurovirulence testing (see graphical abstract).

Spectrum of disease outcomes in mice infected with YFV-17D

The host and viral factors that influence disease outcome during flavivirus infections are not fully understood. Using the live attenuated yellow fever virus (YFV) vaccine strain 17D as a model system we evaluated how viral dose, inoculation route and immunopathogenesis contributed to disease outcome in mice deficient in the type I IFN response. We found that YFV-17D infection of IFN-α/β receptor knockout mice resulted in three distinct disease outcomes: no clinical signs of disease, fatal viscerotropic disease or fatal neurotropic disease. Interestingly, viral load at disease onset did not correlate with disease outcome. However, we found increased immune infiltrates in the brain tissues of mice that developed neurotropic disease. Additionally, mice that developed viscerotropic disease, as characterized by liver and spleen pathology and/or intestinal haemorrhage, had significantly elevated levels of alanine aminotransferase, monocyte chemotactic protein and IFN-inducible protein (IP)-10 as compared with mice with no clinical signs of disease or neurotropic disease. Furthermore, mice treated with recombinant IP-10 throughout YFV-17D infection showed increased mortality and an increased percentage of mice with viscerotropic disease. Our results demonstrated that viral load did not correlate with pathogenesis, and the host immune response played a pivotal role in disease outcome and contributed to YFV-17D pathogenesis in mice.

Dynamic viral dissemination in mice infected with yellow fever virus strain 17D

Arboviruses such as yellow fever virus (YFV) are transmitted between arthropod vectors and vertebrate hosts. While barriers limiting arbovirus population diversity have been observed in mosquitoes, whether barriers exist in vertebrate hosts is unclear. To investigate whether arboviruses encounter bottlenecks during dissemination in the vertebrate host, we infected immunocompetent mice and immune-deficient mice lacking alpha/beta interferon (IFN-α/β) receptors (IFNAR⁻/⁻ mice) with a pool of genetically marked viruses to evaluate dissemination and host barriers. We used the live attenuated vaccine strain YFV-17D, which contains many mutations compared with virulent YFV. We found that intramuscularly injected immunocompetent mice did not develop disease and that viral dissemination was restricted. Conversely, 32% of intramuscularly injected IFNAR⁻/⁻ mice developed disease. By following the genetically marked viruses over time, we found broad dissemination in IFNAR⁻/⁻ mice followed by clearance. The patterns of viral dissemination were similar in mice that developed disease and mice that did not develop disease. Unlike our previous results with poliovirus, these results suggest that YFV-17D encounters no major barriers during dissemination within a vertebrate host in the absence of the type I IFN response.

FLAVIdB: A data mining system for knowledge discovery in flaviviruses with direct applications in immunology and vaccinology

BACKGROUND

The flavivirus genus is unusually large, comprising more than 70 species, of which more than half are known human pathogens. It includes a set of clinically relevant infectious agents such as dengue, West Nile, yellow fever, and Japanese encephalitis viruses. Although these pathogens have been studied extensively, safe and efficient vaccines lack for the majority of the flaviviruses.

RESULTS

We have assembled a database that combines antigenic data of flaviviruses, specialized analysis tools, and workflows for automated complex analyses focusing on applications in immunology and vaccinology. FLAVIdB contains 12,858 entries of flavivirus antigen sequences, 184 verified T-cell epitopes, 201 verified B-cell epitopes, and 4 representative molecular structures of the dengue virus envelope protein. FLAVIdB was assembled by collection, annotation, and integration of data from GenBank, GenPept, UniProt, IEDB, and PDB. The data were subject to extensive quality control (redundancy elimination, error detection, and vocabulary consolidation). Further annotation of selected functionally relevant features was performed by organizing information extracted from the literature. The database was incorporated into a web-accessible data mining system, combining specialized data analysis tools for integrated analysis of relevant data categories (protein sequences, macromolecular structures, and immune epitopes). The data mining system includes tools for variability and conservation analysis, T-cell epitope prediction, and characterization of neutralizing components of B-cell epitopes. FLAVIdB is accessible at cvc.dfci.harvard.edu/flavi/

CONCLUSION

FLAVIdB represents a new generation of databases in which data and tools are integrated into a data mining infrastructures specifically designed to aid rational vaccine design by discovery of vaccine targets.

INDUCED RESISTANCE OF THE CENTRAL NERVOUS SYSTEM TO EXPERIMENTAL INFECTION WITH EQUINE ENCEPHALOMYELITIS VIRUS : III. ABORTIVE INFECTION WITH WESTERN VIRUS AND SUBSEQUENT INTERFERENCE WITH THE ACTION OF HETEROLOGOUS VIRUSES

Although vaccination of guinea pigs with formalin-inactivated Western equine encephalomyelitis virus rendered them specifically immune to an intracerebral challenge dose of 1,000 M.L.D. of Western virus, it failed to protect their central nervous system against the initial effects of the virus: the intracerebral challenge dose was followed by an abortive infection of 20 to 30 hours' duration characterized by fever and histopathological changes which simulated the response at that early stage of non-vaccinated control animals. During the abortive infection of immune animals, virus could occasionally be demonstrated in their brains; indeed, it was detected with about the same frequency it was isolated from brains of similarly inoculated, non-immune guinea pigs during corresponding early phases of the infection. About one week after the abortive infection there was found a marked transitory accumulation of specific neutralizing antibody in the brain tissue. See PDF for Equation equalled at this time 1:1 to 1:10 instead of the value of about 1:300 found under physiological conditions. Guinea pigs which had recovered from an abortive infection with Western virus were resistant for a limited period of time to the effects of intracerebral inoculations of the immunologically distinct viruses of Eastern equine encephalomyelitis or vesicular stomatitis.

The mechanism of active cerebral immunity to equine encephalomyelitis virus; the local antigenic booster effect of the challenge inoculum

The fate of W.E.E. virus has been followed in the brains of mice vaccinated to such an extent that they failed to resist a large intracerebral challenge dose of a viral variant with a rapid rate of multiplication but were fully protected against a similar amount of a "slow" strain. The growth rate of the "fast" variant in vaccinated animals paralleled that in non-vaccinated ones at a slightly lower level. The "slow" strain also multiplied, but its rate of growth was depressed. Nevertheless, it persisted for 4 days at a level 100-fold higher than its initial titer. After the 4th day the virus was no longer demonstrable and was replaced by neutralizing antibody which rose so high that the serum antibody/brain antibody ratio was reduced from a "physiological" value of about 200/1 to less than 10/1. Antibody persisted in brain tissue in high titer until at least 127 days after challenge inoculation. The shift in the serum/brain ratio of neutralizing antibody was paralleled by a similar shift in the ratio of complement-fixing antibody. The neutralizing antibody in brain tissue, like that in serum, followed the "percentage law" on dilution of underneutralized mixtures. In mice immunized with small doses of vaccine, the intracerebral challenge inoculum induced a significantly greater local immune response than in those immunized to a higher degree. Mice with very low grade immunity were found more resistant to large amounts of virus than to small amounts. This "paradoxical" response to challenge was explained as due to the antigenic booster effect exerted by amounts of virus in excess of that utilized to initiate infection which were present in large inocula but absent in small doses. The broader relation of these findings to the problem of antiviral immunity has been discussed.

The pathogenesis of infection with a virulent (CG 179) and an avirulent (B) strain of Newcastle disease virus in the chicken. II. Development of antibody

Circulating antibody appeared in the convalescing NDV-infected chicken concomitantly with the disappearance of virus from the tissues. The antigenic response to the CG 179 and B strains was demonstrated to be approximately equal. The neutralization test in the embryo and the hemagglutination inhibition technique yielded parallel results in the measurement of antibody early in convalescence, but late in convalescence the hemagglutination inhibition titers were relatively lower. This disparity indicates the possible duality of the antibodies. There was a wide ratio between the neutralizing antibody titers found in the brain and in the serum after an asymptomatic infection with NDV. The antibody level in the brain appeared to be related to the extent of virus growth and damage in the central nervous system. It appeared likely that a major factor in determining the virulence of the CG 179 strain was the more rapid attainment in the central nervous system of high virus concentration which outstripped the defense mechanisms of the host.

Experimental rabies in skunks: immune response and salivary gland infection

Groups of striped skunks (Mephitis mephitis) were inoculated intramuscularly with graded doses of street rabies virus. At various intervals after inoculation, saliva and sera were tested for rabies virus and neutralizing antibodies, respectively. Skunks that developed rabies were killed in terminal stages of the disease and the following examinations were made: titers of virus and antibody in submandibular salivary glands and brain, extent of immunofluorescence in submandibular salivary glands, and histologic examination of various tissues. Skunks that received inocula containing 4 x 10(4) to 4 x 10(5) mouse intracerebral lethal dose50 (MICLD50) had detectable serum neutralizing antibodies by 7-12 days postinoculation; however, most of the skunks that received lower doses (40 to 4 x 10(3) MICLD50) did not have detectable serum neutralizing antibodies until clinical signs began. In the salivary glands, slight and extensive immunofluorescence corresponded to high and low titers of tissue neutralizing antibody. Also low viral titers were associated with high tissue neutralizing antibody titers. There was a close correlation between viral titers in right and left submandibular salivary glands. The results suggest that the immune response can impede the process of infection of the salivary glands resulting in lack of antigen or low amounts of antigen in this tissue. This could occur through interference with centrifugal neural transport of virus and/or neutralization of virus during transfer from neural elements to epithelial cells. Lack of infectious virus or low viral titers in salivary glands containing antigen and high levels of tissue neutralizing antibodies can be caused partly by postmortem virus neutralization (during viral titration).