No abstract

We have recently described the production of hepatitis C virus-like particles (HCV-LPs) in insect cells that resemble the putative virions. Here we evaluate the humoral and cellular immunogenicity of the virus-like particles with or without viral p7 protein, a small viral polypeptide that resides between the structural and nonstructural regions of the HCV polyprotein and whose function has not been defined. Immunized BALB/c mice developed high titers of anti-E2 antibodies and virus-specific cellular immune responses including cytotoxic T lymphocytes and T helper responses with gamma interferon production. The virus-like particles without p7 generated a higher cellular immune response with a more T H 1 profile than the particles with p7. Immunization of heat-denatured particles resulted in substantially lower humoral and cellular responses, suggesting that the immunogenicity is strongly dependent on particle Hepatitis C virus (HCV) is a positive-stranded RNA virus that belongs to the Flaviviridae family. The HCV genome contains a single open reading frame coding for a polyprotein that is cleaved into structural and nonstructural proteins by hostand virus-specific proteases. The structural proteins consist of core and 2 envelope glycoproteins E1 and E2. Given the global health burden of HCV infection, there is a paramount need to develop a vaccine against HCV. 1 However, a robust infectious tissue culture system for passaging and expanding the virus and for testing neutralizing antibodies is still lacking. Therefore, newer approaches have to be adopted for HCV vaccine development.Because HCV is an enveloped virus, neutralizing determinants likely reside on the surface of the envelope. The envelope protein E2 of HCV contains highly variable sequences within the N-terminal region (HVR1), which are thought to contain neutralizing B-cell epitopes. 2 Immunization of chimpanzees with recombinant E1/E2 proteins can induce hightiter anti-envelope antibodies but only protects animals from a low-dose viral challenge with the homologous strain. 3 Studies in humans and chimpanzees have indicated that failure to generate multispecific cellular immune responses against HCV in the acute phase of infection is associated with chronicity. 4-7 Therefore, an ideal HCV vaccine should be able to induce strong humoral immune responses against the envelope proteins and to prime broad, HCV-specific T-helper and cytotoxic T-cell responses (for review, see Houghton 8 and Lechmann and Liang 9 ).Virus-like particles are attractive as a recombinant protein vaccine, because they mimic closely the properties of native virions. Papillomavirus-and rotavirus-like particles synthesized in insect cells have been shown to generate protective immunity. [10][11][12] These studies showed that virus-like particles can induce not only high-titer neutralizing antibodies but also strong cytotoxic T lymphocyte (CTL) responses in immunized animals. [13][14][15] Our laboratory has recently reported the synthesis of hepatitis C virus-like particles in insect cel...

Serum TPO level may not be directly associated with thrombocytopenia in patients with chronic hepatitis and liver cirrhosis. In contrast, spleen volume and PAIgG are associated with thrombocytopenia in such patients, suggesting that hypersplenism and immune-mediated processes are predominant thrombocytopenic mechanisms.