Extracellular acidosis enhances Zika virus infection both in human cells and ex-vivo tissue cultures from female reproductive tract

Zika virus (ZIKV) is a flavivirus transmitted by mosquitoes of the genus <i>Aedes</i>, but unlike other flaviviruses, ZIKV can be sexually transmitted by vaginal intercourse. The healthy vaginal pH ranges from 4.0 to 6.0, reaching values of 6.0–7.0 after semen deposition. Here, we report that low extracellular pH values (range 6.2–6.6) dramatically increase ZIKV infection on cell lines of different origin including some derived from the female genital tract and monocyte-derived macrophages. Furthermore, low pH significantly increased ZIKV infection of human ectocervix and endocervix cultured ex-vivo. Enhancement of infection by low pH was also observed using different ZIKV strains and distinct methods to evaluate viral infection, i.e. plaque assays, RT–PCR, flow cytometry, and fluorescence microscopy. Analysis of the mechanisms involved revealed that the enhancement of ZIKV infection induced by low pH was associated with increased binding of the viral particles to the heparan sulphate expressed on the target cell surface. Acidosis represents a critical but generally overlooked feature of the female genital tract, with major implications for sexual transmission diseases. Our results suggest that low vaginal pH might promote male-to-female transmission of ZIKV infection.

寨卡病毒（Zika virus, ZIKV）属于黄病毒属（flavivirus），主要通过伊蚊属（Aedes）蚊子传播，但与其他黄病毒不同，寨卡病毒可通过阴道性行为实现性传播。健康女性的阴道pH值范围为4.0至6.0，在精液沉积后可升至6.0~7.0。本研究证实，低细胞外pH值（范围6.2~6.6）可显著增强寨卡病毒对多种来源细胞系的感染能力，其中包括部分源自女性生殖道的细胞系以及单核细胞衍生巨噬细胞。此外，低pH环境还可显著提升寨卡病毒对离体培养的人类外宫颈与内宫颈组织的感染效率。采用不同寨卡病毒毒株以及多种病毒感染检测手段（包括空斑实验、逆转录聚合酶链式反应（RT-PCR）、流式细胞术与荧光显微镜）开展的实验中，均观察到低pH对病毒感染的增强效应。对相关机制的分析显示，低pH诱导的寨卡病毒感染增强，与病毒颗粒与靶细胞表面表达的硫酸乙酰肝素的结合能力提升密切相关。酸中毒是女性生殖道的关键生理特征之一，但此前常被忽视，其对性传播疾病的发生发展具有重要影响。本研究结果提示，阴道内的低pH环境可能会促进寨卡病毒的男-女性传播。