Human Cytomegalovirus Is Protected from Inactivation by Reversible Binding to Villous Trophoblasts1

Abstract

Human cytomegalovirus (HCMV) is the leading cause of congenital disease in the developed world. Transmission of HCMV to the fetus can occur through the villous placenta. Previously, we have shown that although syncytiotrophoblast (ST) can be productively infected, it is more likely that HCMV reaches the fetus through breaks in the ST than through basal release of progeny virus from infected ST. Progeny virus released on the maternal side could interact back with the ST and accumulate. In pregnancy, the organ distribution of disease burden is dramatically shifted, with the placenta reported as a reservoir for some pathogens. Thus, we propose that the ST layer functions as a viral reservoir, where HCMV is harbored and ultimately protected from degradation. Using primary cytotrophoblasts differentiated into an ST culture in vitro and challenged with HCMV, we have defined reversible binding between the virus and trophoblasts that protects the virus from degradation. This is blocked by treatment with low pH and neutralizing intravenous immunoglobulin. This reversible binding likely is to heparan sulfate proteoglycans, because heparin treatment blocks it. Importantly, we show that bound and released virus maintained in culture for at least 48 h results from inoculum and not progeny virus. Thus, the placenta has the potential to accumulate a relatively high steady-state level of virus within the intervillous space resulting from localized binding and release at the ST. A better understanding of the molecular interactions between HCMV and ST will provide insights regarding interventions to prevent or minimize congenital transmission.

PDGFRα Enhanced Infection of Breast Cancer Cells with Human Cytomegalovirus but Infection of Fibroblasts Increased Prometastatic Inflammation Involving Lysophosphatidate Signaling

“…This occurred before expected viral production, suggesting that input virus remained on the cell surface. Washing at pH 3.0, which removes surface-bound but not internalized virus [36], eliminated infectious virus levels at 12 and 36 h, whereas progeny virus were produced at 48 and 72 h (white bars; Figure 2D).…”

“…A clinical isolate of HCMV, Kp7, was obtained from J.K. Preiksaitis, University of Alberta, Edmonton, propagated in HEL299 fibroblasts [36] and used at <8 passages. A filtered control was generated by passage through a 0.05 µm membrane filter (Millipore Sigma, Tullagreen, Carrigtwohill Co. Cork, Ireland).…”

“…After five washes with HBS, pH 7.4, cells were cultured in DMEM containing 1% FBS for 72 h. Combined cells and culture media were frozen and thawed three times, with vigorous pipetting to facilitate cell lysis and release of viral progeny. Serial dilutions of lysates were added to uninfected HEL299 fibroblasts and cells were stained for IE after 24 h. IE-positive nuclei were expressed as virus/mL based on lysate volume, representing infectious HCMV viral particles [36].…”

Murine Cytomegalovirus Exploits Olfaction To Enter New Hosts

“…A conceptual problem with gastrointestinal infection is that acid inactivates HCMV ( 4 ) and should do so even in preterm infants ( 5 ), as should lipid emulsification by bile: viruses known to infect orally have nonenveloped, acid-resistant virions. Oropharyngeal infection would avoid these insults, but saliva constantly washes the oral contents to the stomach.…”

Human Cytomegalovirus Inhibits the Proliferation and Invasion of Extravillous Cytotrophoblasts Via Hippo-YAP Pathway

“…At present, it remains unclear how HCMV intrauterine infection leads to abnormal development of embryos and fetuses. It is believed that HCMV infection of trophoblast cells is the initiating step of intrauterine infection [17,18]. After implantation of blastocysts, villous trophoblast cells differentiate into villa trophoblasts and EVT.…”