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.