Respiratory syncytial virus and human metapneumovirus : the morphological and transmission studies
Nguyen, Huong Tra
Date of Issue2017-05-17
School of Biological Sciences
DSO National Laboratories
Respiratory syncytial virus (RSV) and human metapneumovirus (HMPV) are the most important viral agents which cause upper and lower respiratory tract infections commonly present in children under the age of five. These infections are also prevalent in the elderly and persons with compromised immune systems. Currently, available drugs for RSV prevention and treatment are not cost-effective (e.g. Palivizumab, ribavirin whose mechanism of action is unproven and has toxic side effects), which makes the treatment of these infections difficult, especially for infections in young children in low in-come families. In the case of HMPV, there is no established prevention and treatment. In this thesis, we studied the transmission pathway of RSV in several permissive cell lines utilizing low multiplicity of infection (moi). We discovered a bi-phasic mode of RSV transmission. At the early infection time from 1 day post infection (dpi) to 3 dpi, there was localized transmission from cell-to-cell, no cell free virus was detected in the culture media up to 2 dpi. At a later infection time (4 dpi, 5 dpi), there was massive cell disruption and detachment releasing a small amount of cell-free virus into the culture supernatant. Cell free virus correlated with changes in cell physiology and increased cytotoxicity. Further, we came to understand RSV transmission using an in vitro system of primary human nasal epithelium cells (hNESPCs) with regard to host responses. Interestingly, NE cells mostly exhibited the mode of cell-to-cell transmission, and event of NE host cell response of p38MAPK activation correlated with the increase in viral particle assembly and changes in host cell physiology. RSV G gene deficiency caused changes in the viral filament morphology, reduced viral transmission efficiency in vitro, suggesting that G protein plays an important role in the virus transmission pathway. By successfully adapting a HMPV strain in culture, we characterized its morphology by imaging analyses and conducted a detailed transmission study. Data suggested the virus likely transmits from cell-to-cell. Host responses arising from HMPV infection showed evidence that the virus triggered the cellular pathway to “turn off” STAT-1 protein level as a strategy to hijack LLC-MK2 cells’ defense pathway in order to penetrate, replicate and thrive, which may be useful in designing future protocols to support HMPV cultivation in vitro.