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Trafficking of the Igalpha/Igbeta heterodimer with membrane Ig and bound antigen to the major histocompatibility

B K Brown1, C Li, P C Cheng

  • 1Department of Cell Biology and Molecular Genetics, University of Maryland at College Park, Maryland 20742, USA.

The Journal of Biological Chemistry
|April 10, 1999
PubMed

The binding of antigen to the B cell antigen receptor (BCR) initiates two major cellular events. First, upon cross-linking by antigen, the BCR induces signal transduction cascades leading to the transcription of a number of genes associated with B cell activation. Second, the BCR internalizes and delivers antigens to processing compartments, where processed antigenic peptides are loaded onto major histocompatibility complex (MHC) class II molecules for presentation to T helper cells. The BCR consists of membrane Ig (mIg) and Igalpha/Igbeta heterodimer (Igalpha/Igbeta). The Igalpha/Igbeta, the signal transducing component of the BCR, has been indicated to play a role in antigen processing. In order to understand the function of the Igalpha/Igbeta in antigen transport, we studied the intracellular trafficking pathway of the Igalpha/Igbeta. We show that in the absence of antigen binding, the Igalpha/Igbeta constitutively traffics with mIg from the plasma membrane, through the early endosomes, to the MHC class II peptide-loading compartment. Cross-linking the BCR does not alter the trafficking pathway; however, it accelerates the transport of the Igalpha/Igbeta to the MHC class II peptide-loading compartment. This suggests that the Igalpha/Igbeta heterodimer is involved in BCR-mediated antigen transport through the entire antigen transport pathway.

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