Essential lymphocyte function associated 1 (LFA-1): Intercellular adhesion molecule interactions for T cell-mediated B cell apoptosis by Fas/APO-1/CD95

B cells are susceptible to Fas ligand (FasL)⁺ CD4⁺ Th1 cell-mediated apoptosis. We demonstrate that blocking the interactions between lymphocyte function associated (LFA)-1 and intercellular adhesion molecule (ICAM)-1 and ICAM-2 completely suppresses Fas-dependent B cell lysis. Antibodies to CD2 and CD48 partially suppress B cell apoptosis, whereas anti-B7.1 and anti- B7.2 antibodies have no effect. Also, B cells from ICAM-1-deficient mice are resistant to FasL⁺ T cell-mediated death. Our results suggest that LFA- 1/ICAM interactions are crucial for Th1 cell-mediated B cell apoptosis and may contribute to the maintenance of B cell homeostasis in vivo.