The JHM strain of mouse hepatitis virus induces a spike protein-specific D-b-restricted cytotoxic T cell response

Cytotoxic T lymphocyte (CTL) activity specific for mouse hepatitis virus (MHV) JHM strain (JHMV or MHV-4) was examined using in vitro stimulated spleen cells derived from immunized C57BL/6 (H-2(b)) mice. Target cells infected with JHMV were specifically recognized; however, analysis of target cells expressing the virus structural proteins via recombinant vaccinia viruses showed no recognition of the viral nucleocapsid (N), membrane (M), small membrane (sM) or haemagglutinin-esterase (HE) proteins. Only target cells expressing the virus spike (S) protein were recognized. Furthermore, the majority of CTL activity was restricted to target cells expressing the MHC class I D-b molecules. Analysis of truncations and deletions of the S protein expressed by recombinant vaccinia viruses and peptide coated targets identified a single antigenic epitope, aa 510-518, conforming to the D-b binding motif. These amino acids are contained within a domain deleted from a number of strains of mouse hepatitis virus, suggesting a role for immune pressure. To determine the potential for CTL specific for an epitope(s) within a non-structural protein, 24 CTL lines were established and characterized. No evidence for the induction of non-specific CTL activity or virus-specific CTL restricted to an epitope in a non-structural protein was obtained. These data indicate that the predominant CTL activity in JHMV-infected C57BL/6 mice is D-b restricted and specific for a single epitope contained within aa 510-518 of the S protein.