Co-ligation of ICAM-1 (CD54) and membrane IgM negatively affects B cell receptor signaling

A possible role of intercellular adhesion molecule 1 (ICAM-1, CD54) in transmembrane signaling was investigated in B cells from the Burkitt lymphoma cell line MTLM4. Cross-linking of membrane IgM (mIgM) induced an increase in intracellular free Ca2+ as a result of the release from intracellular stores and an influx of extracellular Ca2+. When the B cells were incubated with limiting concentrations of anti-IgM, co-ligation of mIgM and CD54, but not CD19, resulted in an inhibition of the Ca2+ response. Separate cross-linking of mIgM and CD54 under these conditions, using isotype mismatched monoclonal antibodies (mAb), did not affect the mobilization of Ca2+. The CD54-mediated inhibition of the Ca2+ response was also observed in the absence of extracellular Ca2+. All CD54 mAb tested (F10.2, F10.3 and F7.11) interfered with mIgM signaling. The results presented in this report imply that CD54 is linked to intracellular signaling pathways and, via co-ligation with mIgM, interferes in the release of Ca2+ from intracellular stores.