Viral replication kinetics and host immune response in neural cells to Zika virus infection : understanding the immune pathogenic mechanisms of Zika virus associated diseases and therapeutic implication of interferon lambda 1

Abstract

Since its emergence in Brazil outbreak in 2015, Zika virus (ZIKV) disease has drew world’s attentiveness. Neurologic manifestations as microcephaly, brain anomalies and congenital contractures in newborn as well as meningoencephalitis, acute myelitis and Guillain-Barré syndrome in adults were found associated with ZIKV infections and expressed a historic switch of ZIKV usual indulgent manifestations to neuro-virulent manifestations. ZIKV is an enveloped, non-segmented, positive sense, single stranded RNA arbovirus. It is a family member of flaviviridae which had a neurotropic history like WNV, JEV, DENV and YFV. Variegated transmission routes have featured ZIKV over other flaviviruses; it can be transmitted via Aedes aegypti mosquito bites, vertically from mother to fetus during pregnancy and sexually. Knowledge regarding ZIKV neuro-immune responses and interactions in the CNS stays elusive. Here I investigated ZIKV replication kinetics and host immune responses in three of the main phenotypes of parenchymal CNS cells; human differentiated astrocytic T98G, neuronal SHSY-5Y and microglia. I found that ZIKV replicated efficiently in the three cell types causing distinct cytopathic effect in microglia and astrocytic cells. ZIKV infected human microglia primarily exhibited hyper-induction of type I interferons (IFN-) and more significantly, type III interferons (IFN-1) of which secretion was confirmed. Inductions of ISGs like ISG-15, PRRs as TLR-3 and RIG-I were also recorded in the neural cells upon ZIKV infection and more prominently in infected microglia. I briefly compared IFNs expressions between ZIKV and WNV infections in the neural cells where I detected IFN- hyper-induction in differentiated neuronal SHSY5Y cells upon WNV infection and not after ZIKV infection. ZIKV infection in the neural cells and majorly in microglia had elicited the expression of proinflammatory cytokines and chemokines which were implicated in brain inflammation like IL-6, IL-8, COX-2, RANTES and IP-10. Hyperinduction of IL-8 in neuronal SHSY5Y superseded its inductions in the other cell types. I could also detect IFNLRs (IL-28RA and IL-10RB) in astrocytic T98G and microglia cells. IL-10RB was detected in neuronal SHSY5Y as well and since IFN-1 is the most known functional type of IFN-s in humans, and since I found hyper-induction of IFN-1 in human microglia upon ZIKV infection. Thus, I investigated the antiviral role of IFN-1 treatment in the neural cells against ZIKV. I found that IFN-1 could suppress ZIKV replication with more than 4 logs in general and in a dose dependent manner in the three cell types. IFN-1 treatment in ZIKV infected microglia could excite the expressions of ISGs like MX-1, OAS-1 and OASL. To conclude, the data here highlight the substantial role of microglia upon ZIKV infection as the prime producer of IFNs especially IFN-1 which could not be suppressed by ZIKV. I also highlight the antiviral role of IFN-1 treatment against ZIKV replication in neural cells as a prospective neuro-therapeutic agent. The inductions of proinflammatory cytokines and chemokines may serve as a contributory factor to understand ZIKV neuro-immune pathogenesis.

(An abstract of 474 words)