An astrocytic binding site for neuronal Thy-1 and its effect on neurite outgrowth.

Thy-1, a member of the immunoglobulin superfamily, is one of the most abundant glycoproteins on mammalian neurons. Nevertheless, its role in the peripheral or central nervous system is poorly understood. Certain monoclonal antibodies to Thy-1 promote neurite outgrowth by rodent central nervous system neurons in vitro, suggesting that Thy-1 functions, in part, by modulating neurite outgrowth. We describe a binding site for Thy-1 on astrocytes. This Thy-1-binding protein has been characterized by immunofluroesence with specific anti-idiotype monoclonal antibodies and by three competitive binding assays using (i) anti-idiotype antibodies, (ii) purified Thy-1, and (iii) Thy-1-transfected cells. The Thy-1-binding protein may participate in axonal or dendritic development in the nervous system.