CD90 (Thy-1), a GPI-anchored molecule and one of the smallest members of the immunoglobulin superfamily of cell surface receptors, consists of a single V-set domain. It is expressed on thymocytes, peripheral T lymphocytes, some intraepithelial T lymphocytes, and neurons of all mouse strains. The monoclonal antibody G7 stimulates T-cell proliferation and IL-2 secretion via signaling through the T-cell receptor/CD3 complex. G7 has also been reported to promote apoptosis of thymocytes and CTL clones and to mediate adhesion of thymocytes to thymic stroma.