Adhesion molecule expression and regulation on cells of the central nervous system

Cellular adhesion molecules were initially defined as cell surface structures mediating cell-cell and cell-extracellular matrix (ECM) interactions. Adhesion molecules involved in immune responses have been classified into three families according to their structure: selectins, immunoglobulin (Ig) superfamily, and integrins. It has been well documented that adhesion molecules of these family members (E-selectin, ICAM-1, and VCAM-1) are expressed on brain microvessel endothelial cells in active lesions of multiple sclerosis (MS) brain. In addition, accumulating data show that glial cells can express some of these adhesion molecules upon activation: astrocytes can express ICAM-1, VCAM-1, and E-selectin, and microglia express ICAM-1 and VCAM-1. In vitro studies show that these adhesion molecules are actively regulated by several cytokines which have relevance to MS or experimental autoimmune encephalomyelitis (EAE). In addition, soluble forms of adhesion molecules have been found in the serum and cerebrospinal fluid (CSF) of MS patients, and may be useful diagnostically. Experimental therapy of EAE using antibodies against several adhesion molecules clearly shows that adhesion molecules are critical for the pathogenesis of EAE. Thus far, the function of adhesion molecule expression on brain endothelial and glial cells has not been clearly elucidated. Studies on the possible role of adhesion molecules on brain endothelial and glial cells will be helpful in understanding their involvement in immune responses in the central nervous system (CNS).