CHANGES IN THE EXPRESSION PATTERN OF BLOOD-BRAIN BARRIER-ASSOCIATED PERICYTIC AMINOPEPTIDASE-N (PAP-N) IN THE COURSE OF ACUTE EXPERIMENTAL AUTOIMMUNE ENCEPHALOMYELITIS

The role of cerebral pericytes in blood-brain barrier (BBB) mechanisms is still a matter of controversy. Because acute experimental autoimmu ne encephalomyelitis (EAE) is characterized by a transient and focal p erturbation of the BBB, we have utilized the model of adoptive transfe r EAE to correlate the expression of the pericytic aminopeptidase N (p AP N) with the acute functional state of the BBB. We demonstrate that a significant downregulation of microvascular pAP N expression occurs, and the observed perturbation of the enzymatic BBB complement seems t o be a sustained effect which persists even after recovery from clinic al disease. At the peak of clinical disease, numerous pAP N expressing invasive cells were detected in white matter of the lumbar spinal cor d. Through the use of a panel of different immunocytochemical markers these pAP N-immunopositive cells were characterized as ED 1-positive, most likely hematogenous macrophages. Activated resident microglial ce lls participate in the EAE-induced inflammatory process to only a mino r extent.