Trafficking of the Igalpha/Igbeta heterodimer with membrane Ig and bound antigen to the major histocompatibility complex class II peptide-loading compartment.
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.
Brown
B K
BK
Department of Cell Biology and Molecular Genetics, University of Maryland at College Park, Maryland 20742, USA.
Li
C
C
Cheng
P C
PC
Song
W
W
D019281:Dimerization; D004705:Endocytosis; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000949:Histocompatibility Antigens Class II; D007136:Immunoglobulins; D008565:Membrane Proteins; D010446:Peptide Fragments