B cell antigen receptors of the IgM and IgD classes are clustered in different protein islands that are altered during B cell activation

15.09.2015

Maity PC, Blount A, Jumaa H, Ronneberger O, Lillemeier BF, Reth M.

Sci Signal. 2015;8(394):ra93.

Sci Signal.           online article

The B cell antigen receptor (BCR) plays an important role in the clonal selection of B cells and their differentiation into antibody-secreting plasma cells. Mature B cells carry on their surface both immunoglobulin M (IgM) and IgD types of BCRs. These receptors have identical antigen-binding sites and are both associated with the signaling subunits Iga and Igb, but differ in their membrane-bound heavy chain isoforms. By two-color direct stochastic optical reconstruction microscopy (dSTORM), we showed that IgM-BCRs and IgD-BCRs reside at the plasma membrane inside different protein islands with average sizes of 150 and 240 nanometer (nm), respectively. Upon B cell activation, the BCR protein islands became smaller and more dispersed such that the IgM-BCRs and IgD-BCRs were found in close proximity to each other. Moreover, specific stimulation of one class of BCR had minimal effects on the organization of the other. These conclusions were supported by the findings from two-marker transmission electron microscopy (TEM) and a Fab-based proximity ligation assays (Fab-PLA). Together, these data provide evidence for a preformed multimeric organization of BCRs on the plasma membrane that is remodeled after B cell activation. These findings where only possible because with the three super resolution methods (TEM, dSTORM and Fab-PLA) it is now possible to better study the conformation and distribution of the BCR on the surface of fixed B lymphocytes at 10-20 nm distances. Previous studies of the B cell surface with the light microscope where restricted by the 250 nm diffraction barrier of visible light. This publication is part of the BIOSS nanoscale explorer program (BiNEP).