T-CELL APOPTOSIS IN INFLAMMATORY BRAIN-LESIONS - DESTRUCTION OF T-CELLS DOES NOT DEPEND ON ANTIGEN RECOGNITION

Elimination of inflammatory T cells by apoptosis appears to play an im portant role in the down-regulation of inflammation in the central ner vous system. Here we report that apoptosis of T lymphocytes occurs to a similar extent in different models of auto immune encephalomyelitis. Apoptosis is restricted to cells located in the neuroectodermal paren chyma, thereby leaving T cells present in the brain's connective tissu e compartments unharmed. Death of T cells in the parenchyma does not d epend on antigen presentation by resident microglial cells or astrocyt es. Adoptive transfer experiments with T lymphocytes carrying a specif ic genetic marker revealed that in the central nervous system these ce lls are destroyed regardless of their antigen specificity or state of activation. Although many of both antigen-dependent and -independent m echanisms in the induction of T-cell apoptosis may act simultaneously, our results suggest that the nervous system harbors a specific, curre ntly undefined, mechanism that effectively eliminates infiltrating T l ymphocytes.