Understanding the mechanisms of antibody-mediated transcytosis of ZIKV within the placenta

体液免疫是机体对黄病毒感染免疫反应的重要组成部分。初次感染产生强大的中和抗体反应，介导病毒控制和保护。日益明显的是，与密切相关的黄病毒株的二次感染可导致免疫交叉反应；然而，对感染结果的后果仍存在激烈的争论和争议。寨卡病毒(ZIKV)是一种蚊媒黄病毒，与登革病毒(DENV)具有高度的序列和结构同源性，自2015年传入巴西以来，导致美洲地区持续流行胎儿先天性畸形。先前的黄病毒暴露与产生与ZIKV结合和/或中和ZIKV的交叉反应抗体密切相关。ZIKV致病机制的一个独特方面是病毒在胎盘内播种感染的能力，然而，经胎盘感染ZIKV的机制尚不清楚。这项建议的总体目标是了解交叉反应抗体如何促进ZIKV跨细胞和胎盘种子感染。胎盘由锚定的绒毛和漂浮的绒毛组成，前者穿透子宫壁，后者沐浴在绒毛间的母体血液池中。最近的流行病学观察发现，在可能接触ZIKV的孕妇中，有20%-50%的孕妇在胎盘中检测到ZIKV RNA。另一份报告发现，在母亲出现寨卡病毒症状后，ZIKV可以在胎盘中持续200多天。我们发现Hofbauer细胞，即位于绒毛间质中的胎儿胎盘巨噬细胞，对ZIKV感染是允许的。为了确定ZIKV进入绒毛间质的潜在机制，我们最近评估了交叉反应性登革热抗体在介导经胎盘感染中的影响。利用体外胎盘移植模型，我们观察到用DENV或ZIKV交叉反应的恢复期血清或单抗产生的ZIKV免疫复合体显著增强了ZIKV对人中期浮动绒毛的感染。与对感染孕妇的胎盘进行组织学分析类似，ZIKV仅在Hofbauer细胞内复制。基于这些观察结果，我们推测Ig G的Fab片段(ZIKV的特异性)和Fc结构域(FcRN和FcγR的亲和力)影响抗体介导的ZIKV胎盘感染。此外，我们认为胎盘的胎龄动态地影响ZIKV转胞和胎盘感染的效率。此外，我们认为胎盘的胎龄动态地影响ZIKV的细胞转运和胎盘感染。在这项建议中，我们试图解决以下悬而未决的问题：1)抗体特异性、亲和力和Fc/FcRN相互作用如何影响ZIKV胎盘感染？2)胎盘胎龄如何影响抗体介导的霍夫鲍尔细胞感染？我们的研究可能会揭示治疗目标，并为开发预防ZIKV感染的疫苗提供见解。

Humoral immunity is an essential component of the immune response to flavivirus infection. Primary infection generates a robust neutralizing antibody response that mediates viral control and protection. It is becoming increasingly apparent that secondary infection with a closely related flavivirus strain can result in immunological cross-reactivity; however, the consequences to infection outcome are hotly debated and controversial. Zika virus (ZIKV) is a mosquito-borne flavivirus, which has a high degree of sequence and structural homology to Dengue virus (DENV), and is responsible for continuing epidemics of fetal congenital malformations within the Americas since its introduction to Brazil in 2015. Prior flavivirus exposure has been strongly associated with generation of cross-reactive antibodies that bind to and/or neutralize ZIKV. A unique aspect of ZIKV pathogenesis is the ability of the virus to seed infection within the placenta, however, the mechanisms of transplacental ZIKV infection are not well understood. The overall goal of this proposal is to understand how cross-reactive antibodies facilitate ZIKV transcytosis and seed infection of the placenta. The placenta is composed of anchoring chorionic villi, which penetrate the uterine wall, as well as floating chorionic villi that are bathed in maternal blood pooling in the intervillous space. Recent epidemiological observations found that between 20-50% of pregnant women with possible ZIKV exposure had detectable ZIKV RNA in the placenta. Another report found that ZIKV can persist in the placenta for over 200 days post mother onset of Zika symptoms. We discovered that Hofbauer cells, fetally- derived placental macrophages located within the villus stroma, are permissive for ZIKV infection. To identify a potential mechanism by which ZIKV gains access to the villous stroma, we recently evaluated the impact of cross-reactive dengue antibodies in mediating transplacental infection. Using an ex vivo placental explant model, we observed profound enhancement of ZIKV infection of human mid-gestation floating chorionic villi with ZIKV immune complexes generated using either DENV or ZIKV cross-reactive convalescent serum or monoclonal antibodies. Similar to histological analysis of placenta from infected pregnant mothers, ZIKV replicated exclusively within Hofbauer cells. Based on these observations, we hypothesize that the Fab fragment (specificity for ZIKV) and the Fc domain (affinity for FcRn and FcγR) of IgG impacts antibody-mediated ZIKV transplacental infection. Moreover, we believe that gestational age of the placenta dynamically influences the efficiency of ZIKV transcytosis and placental infection. Moreover, we believe that gestational age of the placenta dynamically impacts ZIKV transcytosis and placental infection. In this proposal, we seek to address the following outstanding questions: 1) How does IgG antibody specificity, affinity and Fc/FcRn interactions impact ZIKV transplacental infection? and 2) How does placental gestational age impacts antibody-mediated infection of Hofbauer cells? Our studies will likely reveal therapeutic targets and provide insights for development a vaccine to protect against ZIKV infection.