ABSTRACT
Neuroimmunology Laboratory and Multiple Sclerosis Clinic, Centre Hospitalier de l’Universite´ de Montre´al, Hoˆpital Notre-Dame, Montreal, Que´bec, Canada
Activated T cells, regardless of their specificity, cross the blood-brain barrier (BBB) and enter the central nervous system (CNS) under physiological conditions, a process called immune surveillance (1,2). In certain CNSdirected immune diseases such as multiple sclerosis (MS), trafficking across the CNS barrier is enhanced due to actual disruption of the barrier and/or enhanced immune-endothelial cell molecular interactions. This trafficking results in an intense perivascular leukocytic infiltration that appears to underlie the development of the initial disease lesion and, at least, to contribute to ongoing disease progression (demyelination and neuronal cell death) (3). Despite breach in the BBB, leukocyte entry does not appear to be random but rather selective. The MS lesions are predominantly comprised of T cells and activated macrophages, with occasional B cells, and plasma cells (4-6).
