However , the Src family PTK inhibitor PP2 showed limited effects on the infectivity of VSV-EBOV GP in the cell lines expressing DC-SIGN or hMGL. inhibition of the Src family protein PTK pathway, which was also found to be important to promote phagocytosis/macropinocytosis for viral uptake into endosomes. We further confirmed a significant increase of the Src phosphorylation mediated by ADE. These data suggest that antibody-EBOV complexes bound to the cell surface FcRIIa activate the Src signaling pathway that leads to enhanced viral entry into cells, providing a novel perspective for the general understanding of ADE of virus infection. == Author Summary == Antibody-dependent enhancement (ADE), a phenomenon in which viral infectivity is increased by virus-specific antibodies, is observed in vitro for a large number of viruses. For some of these viruses, ADE often become an issue for disease control by vaccination. It has also been shown that some human sera convalescent from Ebola virus disease contain ADE antibodies. ADE has been shown mostly to depend on the cross-linking of virus-antibody complexes to cell surface Fc receptor, which activate various signaling pathways involved in the reorganization of the actin cytoskeleton and membrane remodeling. In this study, we demonstrate that Fc receptor-mediated intracellular signaling is a key factor for ADE of Ebola virus infection. We found that the antibody-virus complexes bound to the cell surface Fc receptors triggered the phosphorylation of particular protein-tyrosine kinases that activated signaling pathways leading to enhanced viral uptake into cells through phagocytosis and/or macropinocytosis. Our study provides new insights into mechanisms of ADE and also offer a potential new cellular target to develop treatments for ADE-associated diseases such as dengue hemorrhagic fever and possibly Zika virus infection. == Introduction == Ebola virus (EBOV), a member of the familyFiloviridae, causes severe hemorrhagic fever in humans and nonhuman primates, with human case fatality rates of up to 90% [1]. EBOV expresses a glycoprotein (GP) that is the only viral surface protein and important for both receptor binding and membrane fusion [2, 3]. EBOV entry is initiated by viral attachment to cell surface molecules such as T-cell immunoglobulin and mucin domain 1 (TIM-1) and C-type lectins [4, 5], followed by internalization of the virus particle into cells via macropinocytosis [68]. In the late endosome, EBOV GP is cleaved by host proteases such as cathepsins L and B [9], exposing the GP receptor binding site that then binds to the receptor, Niemann-Pick C1 (NPC1), followed by membrane fusion [10, 11]. In addition to the direct interaction between GP and host cell receptors, it has been demonstrated that EBOV exploits some GP-specific antibodies for its entry into cells, leading to increased infectivityin vitro[12, 13]. This phenomenon has been described for a number Folinic acid calcium salt (Leucovorin) of viruses and is known as antibody-dependent enhancement (ADE) [1417]. For some of these viruses, ADE has become a great concern to disease control by vaccination. Particularly, convalescent human sera have been shown to contain ADE antibodies [12, 13], raising concerns about potential detrimental effects of passive immunization with convalescent human sera, which is currently under consideration for treatment Folinic acid calcium salt (Leucovorin) of Ebola virus disease. Importantly, it was recently demonstrated that therapeutic treatment with convalescent sera having in vitro neutralizing activities was not sufficient for protection against EBOV infection in nonhuman primates [18]. Although ADE was not evaluated in vitro and any enhanced pathogenicity in the treated animals was not observed, it might be possible that ADE antibodies counterbalanced the neutralizing activity Rabbit polyclonal to USP37 as suggested previously [17]. Folinic acid calcium salt (Leucovorin) Two distinct pathways of EBOV ADE, one mediated by Fc receptors and the other by complement component C1q and its ligands, are known [13, 17]. In particular, the Fc receptor (FcR) is commonly involved in ADE of virus infections [19, 20]. However , the molecular mechanisms underlying ADE-mediated virus entry through FcR are not fully understood. Three classes of FcR, FcRI (CD64), FcRII (CD32), and FcRIII (CD16), are expressed in various human immune cells such as dendritic cells, monocytes, and B lymphocytes [21]. Among these FcRs, FcRII is a key molecule for EBOV ADE of infection in human leukemia K562.