ILA, a member of the human nerve growth factor/tumor necrosis factor receptor family, regulates T-lymphocyte proliferation and survival

ILA, a gene induced by lymphocyte activation, is a member of the human nerve growth factor tumor necrosis factor receptor family and the human homologue of murine 4–1BB. The present study analyzed the role of ILA in the regulation of human peripheral blood T-lymphocyte function. Antibodies raised against different fusion proteins recognized ILA on activated lymphocytes. These antibodies significantly increased anti- CD3--induced T-lymphocyte proliferation. When anti-CD3--stimulated cells were incubated on ILA-expressing CHO cells, proliferation was inhibited. CHO cells transfected with a control construct and not expressing ILA did not reduce T-cell proliferation. A purified fusion protein containing the extracellular domain of ILA and the constant domain of human IgG (ILA-IgG) also inhibited lymphocyte proliferation. Results obtained by 3H-thymidine incorporation were confirmed by cell cycle analysis that showed a decrease in the number of lymphocytes in S phase. Lymphocyte morphology in cultures with ILA-expressing CHO cells was suggestive of apoptosis. Flow cytometry on propidium iodide-stained cells showed a time-dependent increase in the number of hypodiploid apoptotic cells when lymphocytes were cultured on ILA-expressing CHO cells. Internucleosomal DNA cleavage was seen in these cultures, but not in the presence of ILA-negative CHO cells. Studies on the mechanism by which ILA regulates T-cell function showed that ILA-IgG inhibited anti-CD3-induced T-cell proliferation when presented in immobilized but not in soluble form. These results suggest that ILA may act by cross- linking its ligand and thereby inhibit T-cell proliferation.