Co‐Iigation 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.