Analysis of Ebola Virus Entry Into Macrophages

Abstract

Ebolaviruses constitute a public health threat, particularly in Central and Western Africa. Host cell factors required for spread of ebolaviruses may serve as targets for antiviral intervention. Lectins, TAM receptor tyrosine kinases (Tyro3, Axl, Mer), T cell immunoglobulin and mucin domain (TIM) proteins, integrins, and Niemann-Pick C1 (NPC1) have been reported to promote entry of ebolaviruses into certain cellular systems. However, the factors used by ebolaviruses to invade macrophages, major viral targets, are poorly defined. Here, we show that mannose-specific lectins, TIM-1 and Axl augment entry into certain cell lines but do not contribute to Ebola virus (EBOV)-glycoprotein (GP)–driven transduction of macrophages. In contrast, expression of Mer, integrin αV, and NPC1 was required for efficient GP-mediated transduction and EBOV infection of macrophages. These results define cellular factors hijacked by EBOV for entry into macrophages and, considering that Mer and integrin αV promote phagocytosis of apoptotic cells, support the concept that EBOV relies on apoptotic mimicry to invade target cells.

The role of mononuclear phagocytes in Ebola virus infection

“…Consistent with this, it was shown that infection of bone marrow derived dendritic cells with several enveloped viruses, including EBOV, was significantly enhanced by TAM‐mediated inhibition of TLR and IFN signaling . It is reasonable to postulate that TAM signaling in macrophages may play an important, yet currently poorly appreciated, role in EBOV pathogenesis because macrophages up‐regulate Mer expression during maturation, EBOV uses Mer for entry into macrophages, and SOCS1 and SOCS3 are increased upon infection of macrophages with EBOV . In addition, the production of SOC3 through signaling pathways activated by TAM receptors has been shown to lead to enhanced EBOV budding, providing an additional mechanism by which virus production may be increased.…”

“…EBOV enters cells through a complex series of steps that can be broken down into relatively non‐specific extracellular, and highly specific intracellular events. EBOV initially binds to the surface of host cells by engaging either C‐type lectins (CLECs), which bind to N‐ or O‐linked glycans on the heavily glycosylated Ebola glycoprotein, or phosphatidylserine (PS) receptors which mediate clearance of apoptotic bodies . In the context of enveloped virus infections, PS receptors recognize PS in the host‐derived outer membrane of the virion.…”

“…Further, signaling events associated with the use of these receptors likely are critical for regulating filovirus infection in different cell types, but have been poorly explored to date . Whereas receptor redundancy suggests that individual receptors may be dispensable, a recent study using human monocyte derived macrophages (MDMs) found that siRNA‐mediated knockdown of three receptors: Mer, integrin αV, and scavenger receptor A significantly reduced EBOV entry into MDMs . They further found that Axl and TIM‐1 expression is low on human MDMs and siRNA mediated knockdown of these receptors did not reduce EBOV entry, highlighting that these two well‐established surface receptors for other cell types may not be important for EBOV infection of myeloid cells …”

Ebola virus secreted glycoprotein decreases the anti-viral immunity of macrophages in early inflammatory responses

“…Macrophages and dendritic cells (DCs) are early targets in EBOV pathogenesis. Once infected, these cells gain access to the blood and disseminate the virus systemically into tissues and blood vasculature [10][11][12]16]. Viral invasion of endothelia and production of pro-inflammatory cytokines by the circulating infected macrophages and DCs lead to the development of viral hemorrhagic fever that is characteristic of EBOV infection [13].…”

Does Disruption of Integrins Play a Role on Ebola Virus Hemorrhagic Fever Syndrome?

“…Ebola GP expression also led to the down regulation of integrins [12]. Integrand αV was required for efficient GP-mediated transduction and EBOV infection of macrophages [13]. Binding of Ebola virus GP to aVbIII integrins is also shown to prime the endosomal cathepsins, a necessary step in the Ebola virus entry [14].…”