Properties of anti-Lyb-2-mediated B-cell activation and the relationship between Lyb-2 molecules and receptors for B-cell stimulatory factor-1 on murine B lymphocytes

The murine B-cell differentiation antigen Lyb-2 has been shown to be involved in B-lymphocyte activation and has been postulated by some to be related to a receptor for B-cell stimulatory factor I (BSF-1) (H. Yakura et al., J. Immunol. 137, 1475, 1986). Here we have demonstrated that monoclonal antibody (mAB) to Lyb-2 resembles BSF-1 in its ability to activate small resting B cells and enhancement of surface Ia. Anti-Lyb-2 antibodies bound B cells with very high avidity and were able to induce mobilization of cytosolic-free calcium. Anti-Lyb-2 mAB differs from BSF-1 in that BSF-1 but not anti-Lyb-2 is able to synergize with anti-μ in induction of B-cell proliferation. The relation between Lyb-2 molecules and BSF-1 receptors was tested in assays that measure binding of anti-Lyb-2 or BSF-1 in B cells and were found not to compete with each other. It appears that the two B-cell agonists anti-Lyb-2 and BSF-1 may exert their effects on B cells through different cell surface moieties as well as different intracellular pathways.