Protective and pathological roles of virus-specific and bystander CD8+ T cells in herpetic stromal keratitis

Herpetic stromal keratitis (HSK), resulting from corneal HSV-1 infection, represents a T cell-mediated immunopathologic lesion. In T cell transgenic mice on a SCID or RAG knockout background, the T cells mediating lesions are unreactive to viral Ags. In these bystander models, animals develop ocular lesions but are unable to control infection. Transfer of HSV-immune cells into a CD8(+) T cell bystander model resulted in clearance of virus from eyes, animals survived, and lesions developed to greater severity. However, the adoptively transferred CD8(+) T cells were not evident in lesions, although they were readily detectable in the lymphoid tissues as well as in the peripheral and CNS. Our results indicate that viral-induced tissue damage can be caused by bystander cells, but these fail to control infection. Immune CD8(+) T cells trigger clearance of virus from the eye, but this appears to result by the T cells acting at sites distal to the cornea. A case is made that CD8(+) T cell control is expressed in the trigeminal ganglion, serving to curtail a source of virus to the cornea.