The L-selectin antibody FMC46 mediates rapid, transient increase in intracellular calcium in human peripheral blood mononuclear cells and Daudi lymphoma cells.

We report the induction of intracellular calcium mobilization [Ca2+]i in normal peripheral blood mononuclear cells (PBMC) and Daudi cells following binding with the L-selectin monoclonal antibody FMC46. The [Ca2+]i signal was mediated directly by binding of FMC46 without cross-linking antibodies. Increased [Ca2+]i was not induced by other L-selectin antibodies tested (TQ1, Leu8, Lam1.3). The increase in [Ca2+]i was rapid and was blocked completely by BAPTA, an agent which chelates intracellular calcium. The increase in [Ca2+]i was observed in calcium-containing as well as calcium free medium, suggesting that FMC46 caused release of Ca2+ from intracellular stores. In both PBMC and Daudi cells, previous signaling via L-selectin still allowed signaling through cross-linking of surface antigen receptor. These data provide evidence for direct alteration of the state of lymphocytes after ligation of a specific L-selectin epitope. L-selectin-mediated signaling does not desensitize signaling through the antigen-receptor and could therefore play a role in preactivating lymphocytes during endothelial transmigration into lymphoid tissues.