Abstract
Hepatitis C virus (HCV) exploits serum-dependent mechanisms that inhibit neutralizing antibodies. Here we demonstrate that high density lipoprotein (HDL) is a key serum factor that attenuates neutralization by monoclonal and HCV patient-derived polyclonal antibodies of infectious pseudo-particles (HCVpp) harboring authentic E1E2 glycoproteins and cell culture-grown genuine HCV (HCVcc). Over 10-fold higher antibody concentrations are required to neutralize either HCV-enveloped particles in the presence of HDL or human serum, and less than 3-5-fold reduction of infectious titers are obtained at saturating antibody concentrations, in contrast to complete inhibition in serum-free conditions. We show that HDL interaction with the scavenger receptor BI (SR-BI), a proposed cell entry co-factor of HCV and a receptor mediating lipid transfer with HDL, strongly reduces neutralization of HCVpp and HCVcc. We found that HDL activation of target cells strongly stimulates cell entry of viral particles by accelerating their endocytosis, thereby suppressing a 1-h time lag during which cell-bound virions are not internalized and can be targeted by antibodies. Compounds that inhibit lipid transfer functions of SR-BI fully restore neutralization by antibodies in human serum. We demonstrate that this functional HDL/SR-BI interaction only interferes with antibodies blocking HCV-E2 binding to CD81, a major HCV receptor, reflecting its prominent role during the cell entry process. Moreover, we identify monoclonal antibodies targeted to epitopes in the E1E2 complex that are not inhibited by HDL. Consistently, we show that antibodies targeted to HCV-E1 efficiently neutralize HCVpp and HCVcc in the presence of human serum.
Highlights
Hepatitis C virus (HCV),7 a member of the Flaviviridae family, is transmitted during parenteral exposures to infected material, such as contaminated blood or needles
Compounds that inhibit lipid transfer functions of scavenger receptor BI (SR-BI) fully restore neutralization by antibodies in human serum. We demonstrate that this functional high density lipoprotein (HDL)/SR-BI interaction only interferes with antibodies blocking HCV-E2 binding to CD81, a major HCV receptor, reflecting its prominent role during the cell entry process
We reported previously that an interplay between HDL and HCV-E2 leads to infection enhancement of HCV pseudoparticles (HCVpp) [19, 44], an event stimulated by HVR1, and to inhibition of neutralizing antibodies [19]
Summary
Expression Constructs and Production of HCVpp—Expression vectors for the E1E2 glycoproteins of HCV strain H77 (AF009606) and for the HVR1 deletion mutant (⌬G384-N411) were described previously [7, 33]. Binding of soluble E2 glycoprotein to CD81 was performed as described previously [39] and was used to detect the “neutralization of binding” (NOB) activity of antibodies to CD81. For infection assays with HCVpp, the infectious titers were deduced from the percentage of GFP-positive cells, as determined by FACS analysis [7]. Purified HCVpp were injected over AP33 antibody in PBS containing 0.005% P20 surfactant (BIAcore AB) at a flow rate of 5 l/min at 25 °C. Control sensorgrams representing nonspecific binding to the sensor chip surface were automatically subtracted from the sensorgrams obtained with captured HCVpp. Binding assays of HDL, A4 antibody, and CD81-LEL were performed at 25 °C in PBS with 0.005% P20 surfactant at a flow rate of 5 l/min. The surface was regenerated with pulse of 0.025% SDS
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