Expression of intercellular adhesion molecule (ICAM)-1 by B lymphocyte is required for tolerance induction. B-cell-deficient B6 hosts were reconstituted with B lymphocytes by intravenous injection of 10 million splenocytes from normal B6 donors. B-lymphocyte-deficient hosts were resistant to tolerance induction by anti-CD45RB (n=10, diamond), and tolerance was restored by transfer of splenocytes from normal B6 donors (n=7, triangle; P<0.001 vs. anti-CD45RB-treated B-deficient control). However, reconstitution with ICAM-1-deficient cells (n=12, circle) was unable to restore tolerance induction.