Tumor Dormancy and Cell Signaling: Anti-μ -Induced Apoptosis in Human B-Lymphoma Cells is not Caused by an APO-1-APO-1 Ligand Interaction

Signal transduction initiated by crosslinking of antigen-specific receptors on T- and B-lymphoma cells induces apoptosis. In T-lymphoma cells, such crosslinking results in upregulation of the APO-1 ligand, which then interacts with induced or constitutively expressed APO-1, thereby triggering apoptosis. Here we show that crosslinking the membrane immunoglobulin on human lymphoma cells (Daudi) (that constitutively express APO-1) does not induce synthesis of APO-1 ligand. Further, a noncytotoxic fragment of anti-APO-1 antibody that blocks T-cell-receptor-mediated apoptosis in T-lymphoma cells does not block anti-μ -induced apoptosis. Hence, in B-lymphoma cells, apoptosis induced by signaling via membrane IgM is not mediated by the APO-1 ligand.