Ultrastructural observations in hepatitis C virus-infected lymphoid cells

It is currently unclear whether the hepatocellular damage in chronic hepati tis C virus (HCV) infection is produced through the intrahepatic action of the anti-HCV immune response or through a direct cytopathic effect. In orde r to investigate the features of HCV replication (morphogenesis and cytopat hic effect), we studied the infection of a permissive lymphocytic B cell li ne, Daudi cells, which were infected with sera of HCV-positive patients, an d were examined after various time points under electron microscope. Viral genomic RNA was detected by in situ hybridization, and apoptosis with the t erminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL ) method. The amount of viral genomic RNA was observed to increase during i nfection. HCV replicated rapidly, since characteristics of viral morphogene sis resembling those of yellow fever virus in a hepatoma cell line could be found 2 days after infection. These included the following: a) several vir al particles identical in size (about 42 nm) and structure (a spherical 30- nm-sized electron-dense nucleocapsid surrounded by a membrane) to yellow fe ver virus were present in the cytoplasm of cells displaying already typical signs of the early stage of apoptosis; b) numerous membrane-bound organell es and in particular the endoplasmic reticulum and vacuoles were observed; c) proliferation of membranes was apparent; and d) intracytoplasmic electro n-dense inclusion bodies which have been demonstrated to correspond to nucl eocapsids for other flaviviruses were detected. Several cells presented ele ctron-dense areas in the endoplasmic reticulum displaying 30-nm circular st ructures lying among an amorphous material. Striking cytopathic features wi th ballooning, extremely enlarged vacuoles and signs of apoptosis were foun d in cells often containing sequestered aggregates of virus-like particles. By in situ hybridization we found that such enlarged cells contained HCV R NA. Our results thus indicate that the ultrastructural features of HCV vira l particles and their morphogenesis resemble that of yellow fever virus and dengue virus. In Daudi cells, HCV infection seems to rapidly trigger apopt otic cell death, and efficient release of viral particles does not seem to take place. (C) 2001 Editions scientifiques et medicales Elsevier SAS.