Isotype-specific immune response to a single hepatitis C virus core epitope defined by a human monoclonal antibody: diagnostic value and correlation to PCR

A Single Locus Controls Interferon Gamma-Independent Antiretroviral Neutralizing Antibody Responses

An essential step in the development of effective antiviral humoral responses is cytokine-triggered class switch recombination resulting in the production of antibodies of a specific isotype. Most viral and parasitic infections in mice induce predominantly IgG2a-specific antibody responses that are stimulated by interferon gamma (IFN-γ). However, in some mice deficient in IFN-γ, class switching to IgG2a antibodies is relatively unaffected, indicating that another signal(s) can be generated upon viral or parasitic infections that trigger this response. Here, we found that a single recessive locus, provisionally called IFN-γ-independent IgG2a (Igii), confers the ability to produce IFN-γ-independent production of IgG2a antibodies upon retroviral infection. The Igii locus was mapped to chromosome 9 and was found to function in the radiation-resistant compartment. Thus, our data implicate nonhematopoietic cells in activation of antiviral antibody responses in the absence of IFN-γ.IMPORTANCE Understanding the signals that stimulate antibody production and class switch recombination to specific antibody isotypes is crucial for the development of novel vaccines and adjuvants. While an interferon gamma-mediated switch to the IgG2a isotype upon viral infection in mice has been well established, this investigation reveals a noncanonical, interferon gamma-independent pathway for antiretroviral antibody production and IgG2a class switch recombination that is controlled by a single recessive locus. Furthermore, this study indicates that the radiation-resistant compartment can direct antiviral antibody responses, suggesting that detection of infection by nonhematopoietic cells is involved is stimulating adaptive immunity.

Comparative Immunogenicity in Rabbits of the Polypeptides Encoded by the 5' Terminus of Hepatitis C Virus RNA

Recent studies on the primate protection from HCV infection stressed the importance of immune response against structural viral proteins. Strong immune response against nucleocapsid (core) protein was difficult to achieve, requesting further experimentation in large animals. Here, we analyzed the immunogenicity of core aa 1–173, 1–152, and 147–191 and of its main alternative reading frame product F-protein in rabbits. Core aa 147–191 was synthesized; other polypeptides were obtained by expression in E. coli. Rabbits were immunized by polypeptide primes followed by multiple boosts and screened for specific anti-protein and anti-peptide antibodies. Antibody titers to core aa 147–191 reached 10⁵; core aa 1–152, 5 × 10⁵; core aa 1–173 and F-protein, 10⁶. Strong immunogenicity of the last two proteins indicated that they may compete for the induction of immune response. The C-terminally truncated core was also weakly immunogenic on the T-cell level. To enhance core-specific cellular response, we immunized rabbits with the core aa 1–152 gene forbidding F-protein formation. Repeated DNA immunization induced a weak antibody and sustained proliferative response of broad specificity confirming a gain of cellular immunogenicity. Epitopes recognized in rabbits overlapped those in HCV infection. Our data promotes the use of rabbits for the immunogenicity tests of prototype HCV vaccines.

Bacterial cell surface display for epitope mapping of hepatitis C virus core antigen

Cell surface expression of protein has been widely used to display enzymes and antigens. Here we show that Pseudomonas syringae ice nucleation protein with a deletion of internal repeating domain (INC) can be used in Escherichia coli to display peptide in a conformationally active form on the outside of the folded protein by fusing to the C-terminus of INC. Diagnostic potential of this technology was demonstrated by effective mapping of antigenic epitopes derived from hepatitis C virus (HCV) core protein. Amino acids 1-38 and 26-53 of HCV core protein were found to react more sensitively in a native conformation with the HCV patient sera than commercial diagnostic antigen, c22p (amino acids 10-53) by display-ELISA. These results demonstrate that the bacterial cell surface display using INC is useful for peptide presentation and thus epitope mapping of antigen.

Restricted isotypic antibody reactivity to hepatitis C virus synthetic peptides in immunocompromised patients

An enzyme immunoassay based on three synthetic peptides from the core, NS4, and NS5 regions of hepatitis C virus allowed the detection of antibodies in 100% of immunocompetent infected patients and in 91% of immunocompromised patients (hemodialysis and hemophiliac patients). Immune impairment seemed to restrict the spectrum of antibody isotypes reacting to the core peptide.

Improved reactivity of hepatitis C virus core protein epitopes in a conformational antigen-presenting system

Recent studies have identified several epitopes in the N-terminal portion of the nucleocapsid protein which are predominantly recognized by sera of patients infected with hepatitis C virus (HCV). The characterization of the sequences recognized by theses antibodies and the evaluation of their reactivities have been performed mainly with synthetic peptides. However, synthetic peptides are notoriously unreliable as antigens when the immune response is directed against conformational epitopes. In order to improve the detection of antibody responses in HCV-infected patients, we have evaluated the reactivities of three immunodominant regions of the HCV core protein (residues 1 to 20, 21 to 40, and 32 to 46) displayed in a conformation-specific manner on the surface of the Flock House virus (FHV) capsid protein. The results obtained with these proteins in the analysis of 94 serum samples positive by anti-HCV enzyme-linked immunosorbent assay where then compared with those obtained with the corresponding synthetic peptides. The sequence most reactive both with the peptide and with the FHV protein was the region from residues 1 to 20, confirming the low conformational requirements for the display of these residues. On the other hand, the already reported conformational nature of residues 32 to 46 is in keeping with its observed high reactivity when displayed by the FHV recombinant protein and with the low reactivity displayed by its corresponding synthetic peptide. Finally, the high reactivity observed for the chimeric protein displaying the region from residues 21 to 40, as opposed to the results obtained with the synthetic peptide, also suggests that this sequence contains one or more conformational epitopes whose structures cannot be mimicked correctly with synthetic peptides.