Characterization of Components of the Murine B Cell Receptor Complex and Their Role in Anti‐Ig Stimulation

Abstract

Signal transduction in B cells is mediated by B cell receptor (BCR) complexes that are composed of membrane immunoglobulins (mIg) and additional proteins (e.g. Ig-a and Ig-b) that have been implicated with several aspects of B cell activation. In this paper, experiments are described that have been designed to characterize new components of the BCR and to elucidate their involvement in B cell activation directly after the binding of anti-Ig. The data obtained prove the assumption that IgM is degraded after internalization. Neither immunoglobulin nor the Ig-a/b heterodimer are re-expressed after they have disappeared from the cell surface. The newly detected Ig-associated proteins are neither degradation products of immunoglobulins nor different forms of Ig-a or Ig-b. In addition, they are not recognized by antibodies against any of the kinases known to date. The mIg molecules are linked to the cytoskeleton and internalized. On the other hand, the additional Ig-associated proteins as well as the Ig-a/b heterodimer could not be detected in the detergentinsoluble fraction. The former molecules remain on the B cell surface where they are attached to the unaffected isotype and might interact with downstream members of the signalling cascade. In addition, evidence is presented that the internalization of the receptor complex is not necessary for signal transduction and B cell activation. From these results the authors conclude that the BCR complexes are removed from the cell surface after binding of ligands, probably to prevent further activation of this cell, while the Ig-associated proteins interact with the intracellular components of the signal transduction pathway to promote the further activation of the B cells.

Development of a functional in vitro assay as a novel tool for the standardization of allergen extracts in the human system

“…Determination of intracellular calcium mobilization from the endoplasmic reticulum was carried out using FURA‐2 as before (20), with the exception that 50% D 2 O was present in the Tyrode's buffer in which the allergen extracts were diluted. Measurements were carried out with the LS50B spectrometer (Perkin‐Elmer, Rodgau, Germany) and the calcium concentrations were calculated using the FL‐WinLab software provided with the spectrometer.…”