Thy-3, a developmentally regulated T-cell glycoprotein associated to Thy-1 in detergent-resistant membrane microdomains.

The function of the Thy-1 molecule, a major T-cell glycoprotein, is still obscure. Its functional properties might be due to the anchoring via a glycosylphosphatidylinositol group which favors gathering of molecules in functional membrane subregions called microdomains. Using novel monoclonal antibodies, we describe a 53-kDa Thy-1-associated glycoprotein called Thy-3. Thy-3 expression is restricted to T lymphocytes, becomes detectable on double-positive thymocytes, and depends on that of Thy-1. Anti-Thy-3 antibodies immunoprecipitate Thy-1 and Thy-3 or Thy-3 alone in detergents which preserve or disrupt microdomains, respectively. These antibodies induce thymocyte aggregation and interfere with adhesion of thymocytes to a thymic epithelial cell line as previously shown with anti-Thy-1 antibodies. Thus, Thy-3 is a T lineage-specific glycoprotein associated to Thy-1 in membrane microdomains and might contribute to the function of Thy-1 in T-cell differentiation.