Humoral and cellular immune responses to proteins encoded by the hepatitis C virus

Sammanfattning: The hepatitis C virus (HCV) was the first described human pathogen of the hepaciviruses,a new genus within the flaviviridae family. A characteristic feature of HCV is thatit has a high genetic heterogenecity. It is believed that the immune response isof vital importance to prevent, control, and to eradicate HCV infections. However,in most infected persons the HCV infection progress to chronicity. The present researchproject was aimed at further characterizing the interaction between HCV and the infectedhost. The molecular basis for the antibody cross-reactivity between the HCV core anda newly described host-derived gene product, GOR, was investigated. We made two importantobservations. First, the relative antibody avidity was in higher for the HCV core,than for the GOR peptide. Second, the essential residues for antibody binding wereconserved between the HCV core and the GOR peptide. Thus, antibodies specific forHCV core may cross-react with the GOR peptide and their possible role in autoimmunityremains unclear. Different genotypes of HCV may induce type-specific antibodies.We established a method for typing HCV-specific antibodies using differences in theavidity of specific and cross reactive antibody reactivities to type-specific syntheticpeptides. Type-specific antibodies were found in 89% of patients with chronic HCVinfection. The study confirmed that at least three distinct serotypes of antibodiesto HCV exist in Sweden. A major problem in the diagnosis of HCV acute infections is almost total absenceof HCV specific IgM. We analyzed the kinetics of the antibody response in the acuteand chronic phases of HCV infection. The serologic profile during the acute phaseindicated that both the numbers and absorbance levels of HCV core peptide reactivitiesincreased with time. In contrast, patients with chronic HCV infections had multiplehigh level HCV core peptide reactivities. Thus, patients with HCV RNA may be classifiedas acute or chronic phase by using this assay. Little is known about the basic immunogenicity and antigenicity of HCV proteins.Therefore, the immunogenicity and antigenicity of the HCV NS3 protein were characterizedin mice. All tested haplotypes were antibody responders to NS3. The finding of themultiple and crossreactive T-cell recognition sites may explain the high frequencyof antibody responders to NS3 in both infected humans and immunized mice. The murinestudy was extended to analyze the NS3-specific T cell response in HCV infected patientsbefore during and after IFN-a therapy. All patients showed an increased rNS3-specificCD4+ T cell proliferation after IFN-a therapy regardless of the infecting HCV genotypeand the outcome of therapy. Murine T cell responses were analyzed to the short NS4Aprotein. Both human and murine antibodies recognize the same region within NS4A.We also found that, in contrast to NS3, the combination of viral genotype and hostMHC profoundly influences the ability to mount an HCV NS4A-specific immune response. Finally, a NS3-specific single-chain antibody was constructed and expressed inboth bacterial and mammalian cells which recognized the HCV NS3 protein in vitro.This suggested that NS3-specific single-chain antibody could be evaluated for theability to disturb HCV replication in vitro and in vivo. Key words: HCV, genotype, antibody, IFN-alpha, MHC, haplotype, ScFv, peptide,T cell ISBN 91-628-2808-8