Perforin-mediated lysis of target cells is the major
antiviral effector mechanism of CD8(+) T lymphocytes. We have analyzed the role of
perforin in a mouse model for CD8(+) T-cell-mediated central nervous system (CNS) immunopathology induced by Borna disease virus. When a defective
perforin gene was introduced into the genetic background of the
Borna disease-susceptible mouse strain MRL, the resulting
perforin-deficient mice developed strong neurological disease in response to
infection indistinguishable from that of their
perforin-expressing littermates. The onset of disease was slightly delayed. Brains of diseased
perforin-deficient mice showed similar amounts and a similar distribution of CD8(+) T cells as wild-type animals.
Perforin deficiency had no impact on the kinetics of viral spread through the CNS. Unlike brain lymphocytes from diseased wild-type mice, lymphocytes from
perforin-deficient MRL mice showed no in vitro cytolytic activity towards target cells expressing the
nucleoprotein of Borna disease virus. Taken together, these results demonstrate that CD8(+) T cells mediate
Borna disease independent of
perforin. They further suggest that the pathogenic potential of CNS-infiltrating CD8(+) T cells does not primarily reside in their lytic activity but rather in other functions.