title: Immune response to hepatitis B virus core antigen (HBcAg): localization of T cell recognition sites within HBcAg/HBeAg.
abstract: Hepatitis B virus nucleocapsid particles (HBcAg) can function as a T cell-independent antigen when injected into athymic mice. However, immunization of euthymic mice with HBcAg results in dramatically increased anti-HBc titers. Therefore we have examined the murine T cell response to HBcAg in terms of immunogenicity, the influence of H-2-linked genes, and the fine specificity of T cell recognition using synthetic peptide analogs. The HBcAg was shown to be an extremely efficient immunogen in terms of T cell activation as measured by the in vivo dose required to induce T cell sensitization (1.0 microgram), and the minimal in vitro concentration required to elicit interleukin 2 (IL 2) production (0.03 ng/ml). The degree of T cell immunogenicity of HBcAg and its ability to directly activate B cells most likely explain the enhanced humoral response to HBcAg in euthymic mice and HBV-infected patients. The influence of H-2-linked genes on the humoral response to HBcAg was discernable, and high responder (H-2k,s,d), intermediate responder (H-2b,f), and low responder (H-2p) haplotypes were identified. The H-2-linked regulation of the T cell response correlated with in vivo anti-HBc production. Examination of the fine specificity of T cell recognition revealed HBcAg-specific T cells from a variety of strains recognize multiple but distinct sites within the HBcAg/HBeAg sequence. T cell recognition sites were defined by small (16 to 21 residue) synthetic peptides. Each strain recognized a predominant T cell determinant, and the fine specificity of this recognition process was dependent on the H-2 haplotype of the responding strain. For example H-2s,b strains recognized p120-140, H-2f,q strains recognized p100-120, and H-2d mice recognized p85-100 predominantly. Because these sequences are common to both HBcAg and a nonparticulate form of the antigen termed HBeAg, these results indicate that HBcAg and HBeAg are highly cross-reactive at the T cell level although they are serologically distinct. These findings may have clinical relevance, because T cell sensitization to HBeAg and the subsequent seroconversion to anti-HBe status correlates with viral clearance during hepatitis B infection.
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000096:biosynthesis; D000917:Antibody Formation; D000939:Epitopes; D005802:Genes, MHC Class II; D006183:H-2 Antigens / Q000235:genetics / Q000276:immunology; D006512:Hepatitis B Core Antigens / Q000276:immunology*; D006513:Hepatitis B e Antigens / Q000276:immunology*; D008213:Lymphocyte Activation; D051379:Mice; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000914:Antibodies, Viral; D000939:Epitopes; D006183:H-2 Antigens; D006512:Hepatitis B Core Antigens; D006513:Hepatitis B e Antigens; D010446:Peptide Fragments