ACTIVATION OF VIRUS-SPECIFIC MAJOR HISTOCOMPATIBILITY COMPLEX CLASS II-RESTRICTED CD8-CELLS IN CD4-DEFICIENT MICE( CYTOTOXIC T)

Acute enteritic or respiratory disease is a consequence of coronavirus infection in man and rodents. Mouse hepatitis virus, stain A59 (MHV-A 59) causes acute hepatitis in mice and rats and induces a response of major histocompatibility complex (MHC) class II-restricted CD4(+) cyto toxic T cells, protecting mice against acute infection. In the present study we show that MHV-A59 infection of mice that lack a functional C D4 gene activates effector cells of the CD8(+) phenotype. These cytoto xic T cells lyse virus-infected target cells in a MHC class II-restric ted fashion. The results indicate that CD8(+) T cells have the potenti al to utilize MHC class II as restriction element, illustrating that t he immune system can effectively deal with evading microorganisms, suc h as viruses which down-regulate MHC class I.