ROLE OF B-CELL RECEPTOR IG-ALPHA AND IG-BETA SUBUNITS IN MHC CLASS II-RESTRICTED ANTIGEN PRESENTATION

The ability of the a cell antigen receptors (BCRs) to enhance MHC clas s II-restricted antigen presentation was ascribed to mlg-associated Ig alpha/Ig beta heterodimers. The relative role of Ig alpha and Ig beta subunits in antigen presentation was investigated by fusing their cyt oplasmic tails to the extracellular and transmembrane domains of Fc re ceptors, Ig alpha and Ig beta chimera mediate antigen internalization and increase the efficiency of antigen presentation, but they drive an tigens to different endosomal compartments, Furthermore, antigens inte rnalized by either chimera are degraded and presented with different k inetics, The cytoplasmic tail of Iga targets antigen towards a major p opulation of newly synthesized MHC class II located in class II-rich c ompartments, In contrast, Ig beta targets antigen towards a minor popu lation of recycling MHC class II molecules, located in transferrin rec eptor-containing endosomes, Altogether, our data indicate that the com position of BCR could be therefore an important way to modulate the im mune response.