Healthy donors exposed to Japanese encephalitis (JE) virus show a CD8+ T cell response that cross reacts with other flaviviruses. Patients that recovered from JE show a CD4+ T cell response that targets structural proteins of JE virus.

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BackgroundJapanese encephalitis (JE) virus (JEV) causes severe epidemic encephalitis across Asia, for which the live attenuated vaccine SA14-14-2 is being used increasingly. JEV is a flavivirus, and is closely related to dengue virus (DENV), which is co-endemic in many parts of Asia, with clinically relevant interactions. There is no information on the human T cell response to SA14-14-2, or whether responses to SA14-14-2 cross-react with DENV. We used live attenuated JE vaccine SA14-14-2 as a model for studying T cell responses to JEV infection in adults, and to determine whether these T cell responses are cross-reactive with DENV, and other flaviviruses.MethodsWe conducted a single arm, open label clinical trial (registration: clinicaltrials.gov NCT01656200) to study T cell responses to SA14-14-2 in adults in South India, an area endemic for JE and dengue.ResultsTen out of 16 (62.5%) participants seroconverted to JEV SA14-14-2, and geometric mean neutralising antibody (NAb) titre was 18.5. Proliferation responses were commonly present before vaccination in the absence of NAb, indicating a likely high degree of previous flavivirus exposure. Thirteen of 15 (87%) participants made T cell interferon-gamma (IFNγ) responses against JEV proteins. In four subjects tested, at least some T cell epitopes mapped cross-reacted with DENV and other flaviviruses.ConclusionsJEV SA14-14-2 was more immunogenic for T cell IFNγ than for NAb in adults in this JE/DENV co-endemic area. The proliferation positive, NAb negative combination may represent a new marker of long term immunity/exposure to JE. T cell responses can cross-react between JE vaccine and DENV in a co-endemic area, illustrating a need for greater knowledge on such responses to inform the development of next-generation vaccines effective against both diseases.Trial Registrationclinicaltrials.gov (NCT01656200)

Very little information is available on the role of innate immune mechanisms in Japanese encephalitis virus ( JEV) infection. This study was designed to investigate the role of all Pattern Recognition Receptors (PRRs) in JEV infection in a mouse neuronal cell line in comparison to events that occur in vivo, using JEV infected suckling and adult mice. Analysis of mRNA expression was carried out using RT-PCR for detection of PRR genes and their downstream pathway genes, while a PCR array technique was used to examine the complete transcription analysis. Amongst the various innate immune receptors, TLR3 gene exhibited differential expression in JEVinfected Neuro2a, in suckling mice and adult mouse brain cells but not in uninfected control cells. The downstream events of TLR3 were confirmed by increased mRNA expression of IRF3 and interferon-b in JEV-infected Neuro2a cells and suckling mice brain tissue. To confirm the functional significance of this observation, TLR3 gene silencing experiments were carried using specific siRNA in Neuro2a cells. The results revealed a significant enhancement of JEV replication in TLR3 gene silenced JEV-infected Neuro2a cells, thereby suggesting that TLR3 serves a protective role against JEV. The expression levels of other PRRs varied. JEV-infected adult mice showed significant upregulation of TLR2 and MDA5 as compared to JEV-infected suckling mice and Neuro2a cells. In addition, upregulation of Myd88 and IRF7 was also noted in adult mice. These observations, coupled with the fact that adult mice infected with JEV exhibited longer survival rates, suggests that the host antiviral TLR2 response seen in adult mice was eventually countered by the virus by using MDA5 receptor. Our findings suggest that different PRRs appear to be involved in JEV infection in Neuro2a cells and brains of suckling and adult mice.