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 autoimmune encephalomyelitis (EAE) is characterized by a transient and focal perturbation of the BBB, we have utilized the model of adoptive transfer EAE to correlate the expression of the pericytic aminopeptidase N (pAP 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 to be a sustained effect which persists even after recovery from clinical disease. At the peak of clinical disease, numerous pAP N expressing invasive cells were detected in white matter of the lumbar spinal cord. 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 cells participate in the EAE-induced inflammatory process to only a minor extent.