Immunogenicity of JHM virus proteins: characterization of a CD4+ T cell epitope on nucleocapsid protein which induces different T-helper cell subsets.

The CD4+ T-cell-restricted recognition of the structural proteins in the JHM strain of MHV (JHMV) was compared between two mouse strains. Following immunization with inactivated JHMV, all proteins elicited an immune response in both C57BL/6 and BALB/c mouse strains, except the nucleocapsid (N) protein, which was not immunogenic in C57BL/6 mice. T-cell lines and clones were derived from BALB/c mice immunized with UV-inactivated JHMV, to determine the epitope(s) for CD4+ T cells. The N protein appears immunodominant, since all T-cell lines and clones derived therefrom recognized this protein. To locate epitope-containing domains within the N protein, truncated N-protein fragments expressed in vaccinia constructs were used to stimulate the T-cell clones. Five independent T-cell clones recognized three separate N-protein domains: 1-133, 134-249, and 250-306. Since three of five clones recognized the last domain, its sequence was studied in more detail by constructing overlapping synthetic peptides covering this region. A single epitope was localized within the peptide comprising the N-protein residues 266-279. Its restriction element was identified as I-E(d) using mAb to I-E(d) and I-A(d). In addition, peptide N266-279 contains the motif for binding to I-E(d). This peptide elicited proliferative responses following immunization with JHMV, confirming its recognition in the complete virus. In addition, peptide N266-279 was recognized by T-cell clones that express differences in cytokine profile as well as in TCR Vbeta usage.