A serum protein factor mediates maturation and apoB-association of HCV particles in the extracellular milieu

Background & Aims In the sera of infected patients, hepatitis C virus (HCV) particles display heterogeneous forms with low-buoyant densities ( 1.08) and poor/no association with apoB. We aimed to elucidate the mechanisms of lipidation and to produce HCVcc particles resembling those in infected sera. Methods We produced HCVcc particles of Jc1 or H77 strains from Huh-7.5 hepatoma cells cultured in standard conditions (10%-fetal calf serum) vs . in serum-free or human serum conditions before comparing their density profiles to patient-derived virus. We also characterized wild-type and Jc1/H77 hypervariable region 1 (HVR1)-swapped mutant HCVcc particles produced in serum-free media and incubated with different serum types or with purified lipoproteins. Results Compared to serum-free or fetal calf serum conditions, production with human serum redistributed most HCVcc infectious particles to low density ( . Moreover, compared to Jc1, we detected higher levels of H77 HCVcc infectious particles in very-low-density fractions, which could unambiguously be attributed to strain-specific features of the HVR1 sequence. Finally, all 3 lipoprotein classes, i.e ., very-low-density, low-density and high-density lipoproteins, could synergistically induce low-density shift of HCV particles; yet, this required additional non-lipid serum factor(s) that include albumin. Conclusions The association of HCV particles with lipids may occur in the extracellular milieu. The lipidation level depends on serum composition as well as on HVR1-specific properties. These simple culture conditions allow production of infectious HCV particles resembling those of chronically-infected patients. Lay summary Hepatitis C virus (HCV) particles may associate with apoB and acquire neutral lipids after exiting cells, giving them low-buoyant density. The hypervariable region 1 (HVR1) is a majorviral determinant of E2 that controls this process. Besides lipoproteins, specific serum factors including albumin promote extracellular maturation of HCV virions. HCV particle production in vitro , with media of defined serum conditions, enables production of infectious particles resembling those of chronically infected patients.