A cell surface antigen expressed by astrocytes and their precursors

Increasing evidence suggests that astrocytes of the mammalian CNS are a heterogeneous population of cells that express a number of common characteristics. In most cases, astrocytes or their precursors contain a class of intermediate filaments, composed in large part of glial fibrillary acidic protein (GFAP). While the expression of GFAP immunoreactivity is a specific characteristic of astrocytes in the vertebrate CNS, not all astrocytes contain detectable levels of glial filaments, particularly during early development. We have isolated a monoclonal antibody termed 7B11 which binds to the surface of astrocytes and glial precursors, but not to other major types of neural cells. The 7B11 antigen is expressed by astrocytes in the adult CNS in vivo and in cultures of developing CNS tissue, but not on cells of the peripheral nervous system. During early development, 7B11 immunoreactivity appears prior to the expression of GFAP and is retained as punctate staining on the surface of most classes of astrocytes. During CNS maturation, however, 7B11 immunoreactivity is lost from the surface of Bergmann glia in the cerebellum, suggesting that differentiative events lead to functionally and antigenically distinct classes of CNS glial cells. In the adult spinal cord, biochemical analysis suggests that the epitope recognized by 7B11 is associated with a group of polypeptides of apparent molecular weights 200-160, 140, and 92 kD. The cellular distribution of 7B11 expression suggests that astrocytes and their precursors share a distinct cell surface antigenic property and that the expression of 7B11 immunoreactivity may be a useful operational marker for astrocytes in the absence of detectable GFAP expression.