Regulation of T lymphocyte function by glycosylphosphatidylinositol (GPI)-anchored proteins.

Monoclonal antibody binding to GPI-anchored proteins, e.g. Thy-1 and Ly-6, on the surface of T lymphocytes usually leads to stimulation of interleukin-2 production. This phenomenon is dependent upon expression of the zeta-chain of the T cell receptor complex and requires the GPI anchor. Recent studies suggest that this activation may proceed through a common pathway resulting in tyrosine phosphorylation of intracellular substrates and association of various GPI-anchored proteins to src-family tyrosine kinases. Several models are discussed to explain the signaling capabilities of GPI-anchored proteins. In contrast, under some experimental conditions antibody binding to selected GPI-anchored proteins, i.e. Ly-6A/E and sgp60 (CD48), leads to inhibition of T cell activation. Furthermore, induction of Ly-6A/E expression on CD4 effector T cells correlates with a decreased capacity to secrete IL-2. These latter results suggest that Ly-6A/E may also function to down-regulate an immune response.