Intranasal mouse hepatitis virus-1 (MHV-1) infection of susceptible mouse strains mimics some important pathologic features observed in the lungs of severe acute respiratory syndrome (SARS)-coronavirus - infected humans. The pathogenesis of SARS remains poorly understood, although increasing evidence suggests that immunopathology could play an important role. We previously reported that the adaptive immune response plays an important protective role in MHV-1 - infected resistant B6 mice and that both CD4 and CD8 T cells play a significant role in the development of morbidity and lung pathology following intranasal MHV-1 infection of susceptible C3H/HeJ and A/J mice. In this study, we have identified novel CD4 and CD8 epitopes in MHV-1 - infected susceptible and resistant strains of mice. Susceptible C3H/HeJ mice mount robust and broad MHV-1 - specific CD4 T cell responses, whereas in resistant B6 mice, Ag-specific CD8 T cell responses dominate. We also show that previously immunized susceptible C3H/HeJ mice do not develop any morbidity and are completely protected following a lethal-dose MHV-1 challenge despite mounting only a modest secondary T cell response. Finally, we demonstrate that the resistance displayed by B6 mice is not solely accounted for by the elaboration of a broad and vigorous MHV-1 - specific CD8 T cell response, as MHV-1 infection of C3. SW-H2b/ SnJ mice, which mount an equally robust CD8 T cell response of the same specificity, is still associated with significant morbidity. Thus, identification of novel CD4 and CD8 T cell epitopes for MHV-1 permitted high-resolution analyses of pulmonary T cell responses in a mouse model of SARS.
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